Is it possible to have the L28's cylinders sleeved to compensate for excessive wear/boring? I understand this is regular fare for diesels, but the gas engines?

Yeah, any machine shop should be able to do that.

For the cost it's cheaper to get a different block.

THey're a rare commodity here, for some reason (at least in good shape) and I'm not willing to have it shipped.

If they can do it and you find out the cost per cylinder shipping may look cheap! Last I saw it was around $75 + per cylinder and that is if there is enough block left to put one in.

Lance is right, but be careful about buying another block. You may end up with one worse than yours.