Although it's neither feat nor psionic power, the effect you want's available as a low-priced magic item and a mid-level spell.
The Magic Item
The Web site Athas.org teeters on the extreme edge of official, saying that it
is recognized by WotC as the Official Dark Sun site on the internet. Content created on the official website is considered to be derivative work (as it is based on the intellectual property owned by Wizards of the Coast). This means that fan-created add-ons (such as new net books, adventures, etc.) are jointly owned by both Wizards of the Coast and the creator; neither can do anything outside the official website without the permission of the other. [sic]
Thus in the unlikely event the DM can be convinced to allow material from Athas.org (Comments' experiences say most DMs won't), the Athasian Emporium contains the
Third Eye Long Touch
The wearer of this kind of third eye [MIC 140] can use his touch attacks as if they were ranged touch attacks with a 30-foot range increment. It does not actually grant reach, and so does not help provide a flanking bonus or allow the wearer to make attacks of opportunity at any range greater than normal. The wearer uses his normal melee attack bonuses and normally affects the target with the effect of his touch if it hits, though the target of the attacks can benefit from cover or concealment.
Faint telekinesis; ML 1st; Craft Universal Item, far hand; Price 2,000 Cp.
The notation Cp--not to be confused with cp meaning copper pieces--stands for ceramic pieces, the Dark Sun campaign setting's equivalent to gold pieces. (Yes, in the Dark Sun campaign setting, the most commonly encountered currency isn't mined but baked. Just go with it.)
On the right face, this is a ridiculously useful item at a very low price.
The Spell
The 5th-level Sor/Wiz spell greater spectral hand [necro] (Dragon #303 36-7) is like the 2nd-level Sor/Wiz spell spectral hand [necro] (PH 282) except that "the hand can deliver any touch range spell of 6th-level or lower. In addition, if [the caster has] a supernatural effect tied to [his] touch, such as a paralyzing touch, the hand can deliver that effect as well." Further, the hand's 3d4 hp total is subtracted from the caster's own. (A non-greater yet still spectral hand has, instead, its 1d4 hp subtracted from its creator's hp.)
Just this far from fitting into a wand, one would have to cram the spell into a custom staff of greater spectral hand (34,050 gp; 4 lbs.) (50 charges) or talk to the DM about a different, even more custom magic item.
This is, admittedly, not a ranged touch attack and instead a means to use a touch attack at range, which may be close enough.
Best Answer
Natural weapons do not use dexterity for attack rolls “naturally;” a creature needs to take Weapon Finesse in order to do that. For example, see the cat; it gets Weapon Finesse as a bonus feat.
Touch attacks are not natural weapons; they do not follow the rules of natural weapons, but rather of “weapon-like spells,” which are mostly similar to manufactured weapons. For example, you don’t automatically get one attack/touch-effect you have available, but you could conceivably get iteratives if you had a touch-effect that lasted, such as chill touch (you cannot with charnel touch because it is explicitly 1/round, but you could use it for one attack and then use your iteratives for attacks with other weapons).
In particular,
Complete Arcane pg. 73.
Unfortunately, the only way I know of for getting Weapon Finesse without taking the feat only works for weapons, by getting a feycraft weapon.