good small forwards are usualy a result of training some as a guard and some as forwards.
buying a good SF can be very expensive, because a SF has to be good in almost everything
some suggestions:
1. if you play one type of offense, like for example, inside focoused offense, you can buy a PF with good outside deffense. and vice versa, you can but a good SG with good inside deffense and rebounding
2. if you can wait a bit, you can buy a good PF with good outside deffense and train his as a guard for a while. but if he is tall he will learn slower....
3. if you have the money, you can look for players whow are good in any type of deffense, rebounding, and can shoot inside and out... it should cost a lot