There is also the SupraTurbo, which is a 28mHz accelerator that plugs into the sidecar slot, and will take (I think) up to 8 Mb of extra memory, if you can still find the chips.
It's not quite in the '030 league, but is probably easier to find.
Also, it can be powered externally, which helps take the load off "The Brick". (BTW, if anyone knows for sure what voltage it uses, please let me know, as I don't have a PSU for mine, and I'm not prepared to risk frying it. :-)
(I assume it's 5 volts, but....)