if you're looking for a 4-2 these are the options that I know of:
1) the jardine system you mentioned. I've seen used ones on ebay.
2)i think Mac made turnout mufflers that mated to the original headpipes. Pretty sure they don't make it anymore.
3) I had a 4-2 system on my bike made by MC. It's been a while but NOS sets used to pop up on ebay. Here's the system on my bike:
As gordon said, I think a low sound would be pretty difficult to find with an engine as small and revvy as the 350f.