Without the old tubes you are not going to be able to find a pattern to make your own tubes. Next cheapest is going to be to find a boat repair place that specializes in RIB's and see if they saved a pattern, as most will once they have made a set of tubes for each individual boat. Luxury RIB Tenders come to mind but mostly because he is a Youtuber.
https://www.luxuryribtenders.com/copy-of-boats-tubes Expect a minimum of $4,000 US for a set of tubes made and shipped. Not sure you will be able to turn a profit unless you can pattern and make the tubes yourself which although not super hard is a rather large job. Buying bulk Hypalon (Orca) would allow you do build a few sets of tubes for a reasonable amount IF you have a pattern. The glue used isn't cheap either at around $800 US for 5 gallons.
There could well be someone in Mexico who makes tubing sets.