Bachman Pawn and Gun -
http://www.bachmangun.com - had a SP89 -
http://www.unsuave.com/~hkpro/sp89.htm - at the gun show in Houston this weekend. It was $3,600.
Special Weapons is building a MP5 replica that is less expensive -
http://www.specialweaponsllc.com/
Finally, HK may offer a civilian version of the UMP later this year or early next year. You can see the prototype at
http://www.unsuave.com/~hkpro/update.htm