The 3-position functionality is in the valve spool body itself, not in the base, so there is not a simple base swap that would provide that function. You would need a genuine 3-position valve. Here is one
http://cgi.ebay.com/4-Way-3-Position...item3ca6c9c3e1
and there are others listed of larger sizes. They do not tend to be cheap, even on Ebay. I would say the only 'inexpensive" option would be if you were lucky enough to find a used one from a distributor or an outfit that breaks down and sells parts from industrial equipment.
My advice would be to not hold a grudge against single-solenoid valves. They are probably the most common type of solenoid valve ever used in every kind of commercial and industrial application. The Festo and other single-sol valves that have been included in past FRC KOPs are proven industrial valves made for long service. If you have had a bad experience with them then there was something wrong with it and you had bad luck. What problems have you had? We have used them multiple times with no trouble. They provide the functionality you are looking for with the limitations you have, and if you are with a team that has a collection of past KOP parts you probably have them already. Unless your project is life-or-death critical or will see extremely harsh or long service, they should work fine. If you have them, it costs nothing to try them first.