If you want the same string that came on it, contact Ron and find out. Depending on how odl the string is, it could have been the current string maker or a different one. If you bought the bow used, it may have been someone else who made it. Making a 6-8 strand 450+ string isn't rocket science.
If your bow is FF compatible, any of the string materials available will be safe as long as the string is made properly. 450+ has the least stretch/creep of any material on the market, so it should be fine for anything.
My personal preferances are 8125G, 8190, and Dynaflight '97.
Chad