It looks like the "rom laboratory" site is back up again,
http://nintendoallstars.w.interia.pl/m4_mmc3.htm
unfortunately it is a .gif chart so I can't copy and paste, but there is actually a listing for "samurai pizza cats"
it is 128kB of PRG and 128 kB of CHR, vertical mirroring, no battery.
This is actually the exact same specs as Super Mario Bros. 2, (Super Mario USA)
as well as a number of other carts.
mirroring is trivial to change; it is just a blob of solder, and I think any cart with the same or larger ROMS will work fine (smaller ones may not have all the address lines hooked up, but will prolly have them there anyway and work OK)
So, get a copy of super mario 2 and identify and chop/desolder the ROMS and you should be in business.
There are a couple of lines you need to cut and swap with small wires; I guess by the time MMC3 games came out they did not use JEDEC standard ROM pinouts as an anti-piracy measure or something.
I assume you are in the USA, you should be able to get 27C010 EPROMs (128K x 8, 1Mbit, there are lots of equivalent parts) for 1-3 bucks each. Try www.bgmicro.com, they are a good surplus shop. They are reusable if you find them on old motherboards or equipment, you need access to a UV eraser or something with short-wavelength germicidal UV bulbs.
These are EPROMS, so they would have to be programmed. Almost any college or university or business that does embedded systems will have a universal programmer than can program almost any EPROM in a few seconds each.