Access keyboards appear frequently on eBay.co.uk.
You'll need a PC with a ps2 port, not an adapter. Or, hold out for a USB one. There's a guide somewhere on Deskthority.
Tipro are easier to program and support more layers than access.
Ps2 Access are nkro, tipro are 2kro.
Bear in mind that if you program in layer, you won't be able to activate it on one keyboard, and use it on the other.
Another alternative would be to get a larger keyboard, and move the modifiers to the middle, much like the type matrix.