6th-level barbarians with the Ancestral Guardian archetype have the Spirit Shield feature (Xanathar's Guide to Everything, p. 10):

Beginning at 6th level, if you are raging and another creature you can see within 30 feet of you takes damage, you can use your reaction to reduce that damage by 2d6.

When you reach certain levels in this class, you can reduce the damage by more: by 3d6 at 10th level and by 4d6 at 14th level.

3rd-level fighters with the Psi Warrior archetype have the Psionic Power: Protective Field feature (Tasha's Cauldron of Everything, p. 43):

When you or another creature you can see within 30 feet of you takes damage, you can use your reaction to expend one Psionic Energy die, roll the die, and reduce the damage taken by the number rolled plus your Intelligence modifier (minimum reduction of 1), as you create a momentary shield of telekinetic force.

1st-level fighters and 2nd-level paladins have the Fighting Style: Interception feature (Tasha's Cauldron of Everything, pg. 41, pg. 53):

When a creature you can see hits a target, other than you, within 5 feet of you with an attack, you can use your reaction to reduce the damage the target takes by 1d10 + your proficiency bonus (to a minimum of 0 damage). You must be wielding a shield or a simple or martial weapon to use this reaction.

6th-level sorcerers with the Clockwork Soul archetype have the Bastion of Law feature (Tasha's Cauldron of Everything, pg. 69):

You can tap into the grand equation of existence to imbue a creature with a shimmering shield of order. As an action, you can expend 1 to 5 sorcery points to create a magical ward around yourself or another creature you can see within 30 feet of you. The ward lasts until you finish a long rest or until you use this feature again.

The ward is represented by a number of d8s equal to the number of sorcery points spent to create it. When the warded creature takes damage, it can expend a number of those dice, roll them, and reduce the damage taken by the total rolled on those dice.

6th-level warlocks with the Fathomless patron have the Guardian Coil feature (Tasha's Cauldron of Everything, pg. 73):

Your Tentacle of the Deeps can defend you and others, interposing itself between them and harm. When you or a creature you can see takes damage while within 10 feet of the tentacle, you can use your reaction to choose one of those creatures and reduce the damage to that creature by 1d8. When you reach 10th level in this class, the damage reduced by the tentacle increases to 2d8.

These features reduce any damage type, although the modifier is not a fixed number (and it uses reaction, so it can only be done once per round). You can have a mix of "weapon" and "magic" damage type as your scenario suggested: bludgeoning+fire.

There currently is no method for this

While the Unearthed Arcana Lore Wizard created a method to change spell damage types, it only included spells that cost a spell slot, so cantrips like Eldritch Blast were not included.

In terms of changing a damage type for any spell, that was your only option.

However, even if you did utilize that, you really have to be careful in multiclassing Unearthed Arcana classes - those weren't tuned for multiclassing and combining a UA class with a UA invocation is treading into risky waters.

DM's choice to change it

A DM could provide EB as fire instead of force. Ultimately, it's not a big deal, but it may become a decision you regret because there are many monsters with fire resistance/immunity and very few force resistant/immune.

Changing for flavor

While Mustang does use actual fire here, you could just 'flavor' the look of your eldritch blast to be a fire-looking effect - but that it does just deal force damage. If you don't change the actual mechanics (damage type), then you can change your narration for it - and maybe just for when you use the invocation.

A build challenge

Instead of going with your current build, you could do a Sorcerer build that has fire bolt and the Metamagic Quickened Spell so that you can cast the cantrip fire bolt and follow it with a quickened fireball bonus action.

If you want to minimize risk here with fire being often resisted, you could also take the Elemental Adept feat (PHB, p. 166) and bypass fire resistance.

• Spells you cast ignore resistance to fire damage. In addition, when you roll damage for a spell you cast that deals fire damage, you can treat any 1 on a damage die as a 2.

• You can select this feat multiple times. Each time you do so, you must choose a different damage type.