Here is a really good place to get some patches or banks. Note that the banks will replace the sounds in your USER bank. So make sure you save your current User bank onto disk "BEFORE" you play the .mid file.
http://users.netconnect.com.au/~ahair/jvxp/
This one is not as good but you might want to see it;
http://www.diku.dk/students/kroll/superjv/ And one other one that is really good;
http://home.sol.no/gkilsti/ Hope i helped. I'm a beginer as well so any info i get is really helpful.