I think your only option is to call Bassani and order them. Measure the available length in the 3.5" exhaust tip so you can tell them what you need (18" long baffle is what I have read is 'standard').
The baffles make a huge difference. Their baffles for their 3.5" tips fit the Magnaflow tips perfectly. And, agreed with the above, the only place to get them is calling them direct. Price used to be $25 each but has gone up due to increased demand by us with Magnaflow owners looking to quiet them down (aka, the "Magnaflow minority"...). I love mine.