Hellsing pistols?
 

Does anyone know if there are any kits to make Hellsing pistols? Or can anyone make one?

I don't think any exist.

The only one I could see being doable would be the .454 Casull...the other huge one he gets later on (forgot the name) would be really hard to do, just because of the size of the slide.

You would have to extend the slide waaaay out for the Casull, so an NBB (like a TM Socom Mk23) would probably be the only gun that could possibly fit it.

They seem based on the Tranter, and those were .577 caliber.
Nope, nothing airsoft comes close.

I have only seen the kit for the Jackal from a Japanese company called Poseidon. Here's a link:

http://www.poseidon.co.jp/2F/g-jackal/bj1.html

There's even a link for a short mpg that shows it in action. According to the translation, it uses a Tokyo Marui M9 to make it a working GBB. However, it does state that they are not selling the item overseas.

They also have the Casull as a non-firing resin model
http://www.poseidon.co.jp/6F/alucard/ar_1.html
however that one is out of production...