Mike, townhouses are usually separated, as you know, by firewalls, which, in order to be fire-rated, can't have any holes on the blocks, so penetrations for receptacle boxes are not allowed. In such cases, the options left to the builder and electrician are:
1) Use furring strips, which is 99% likely what you have, which allow about 3/4 in. of space. It is not likely that this wall is insulated, as the other side of the wall is also living space. There are boxes shallow enough to fit into a wall space this thin.
2) Go ahead and use full studs, which allow plenty of depth for standard wall boxes, but make the unit a couple of inches narrower, although I'm sure the cost is more important. It's doubtful you'll find insulation here, either.
My fiance owns a townhouse that has the first option, and the receptacle along that wall is a floor mounted, brass-plate-covered one. There is the possibility that the floor framing has gaps along the block that you might fit a wire into, between the last joist and the block. If not, you should be able to drill up or down into that space, as long as you stay within that 3/4 in. gap against the block.
You didn't mention if you want to go up or down, so I'll leave further detail for another reply.
