2 things: sound enhancements (accutronics' mfr) was recently sold to belton. shouldn't be a problem getting stuff, but just in case, go through your music dealer channels.
another is that as long as the reverb transformer impedances matches the reverb circuit (and is even available), you should be fine ordering a reverb tank. the part code fo the mesa mark iv and v tank is 9AB2A1B. here's the description of the code for the accutronics tanks:
http://www.accutronicsreverb.com/Type9.htm
you're pretty much constrained to the type 9 tanks cause that's the sizing of the cutout. so what you wanna do is see if you can get a different 4th digit, which is the decay time, i.e. 1 for you since you want short. so you can find something like a 9AB1A1B. i don't know if it's even an available part. contact them and see. hopefully you know what i'm saying.