The character should be able to treat light blades as implements (via the Swordmage feature or apposite feat). Then, simply inferring from the rules:
Spiked Chain TrainingDDI
• Wielding a double weapon is like wielding a weapon in each hand. [...] The two ends of a double weapon can have different proficiency bonuses, damage, properties, and weapon groups. The weight and price entries represent the total for the weapon, rather than only one side.
• An enchanted double weapon gains all benefits of the enchantment on each end (even if one end would not normally qualify for the enchantment). This does not increase the frequency of use of any power possessed by the item; if you wield a double weapon with a daily power you can still only activate that power once per day.
[Multiclass Spiked Chain]
Prerequisite: Dex 13
Benefit: You gain proficiency with the spiked chain. You can treat the spiked chain as a double weapon. As a double weapon, each end of the spiked chain is a light blade and deals 2d4 damage. The primary end gains the stout property, and the secondary end gains the off-hand property.
Note to readers: spiked chains fall in the Flail weapon group. Is the Spiked Chain Training feat that makes them Light Blades too.
- being both ends of the spiked chain treated as light weapons,
- because of both ends of an enchanted double weapon gains the enchantment's properties,
- being light blades an implement for the character, and
- possessing the Dual Implement Spellcaster feat
the character may apply enhancement bonus damage to her implement arcane attacks from both ends of the double weapon.
Since sometime in 2009, if you have proficiency in an implement type from any source, you can use that implement with any power that has the implement keyword.
The easiest MC for a cleric to qualify for that provides Staff implement proficiency is Acolyte of Divine Secrets (mc invoker), which requires 13 wisdom and gives you access to staves and rods, as well as Hand of Radiance, which is exceptional for minion popping. The wasted duplicate training in religion is sad, but hardly a deal-breaker.
Sentinel Initiate is another option, at the same requirements, providing you with nature training, staff proficiency, and a 1/day extra healing word in an encounter.
MC Wizard does also work here, but your INT is probably not attack-calibur, so the at-will-as-an-encounter power is substantially less of a draw on that end.
Clerics start with proficiency in staves as weapons (they're a two-handed simple weapon), and yes, quarterstaves can be used as staff implements and staff implements can be used as quarterstaves. Keep in mind that you can use staves as implements in one hand, but you will need to hold it two-handed to make weapon attacks with it. This is only an issue if you wanted to hold a shield or second implement in your off-hand.
Most of the musical instrument magic items are flutes, lutes, harps, horns, lyres, sitars, mandolins, bandores and drums. They are usually listed under wondrous items and will clearly say that a bard can use them as an implement and how they are used as such. You can find them in the PHB2.