Do you have "SayWeee!" delivery in your city? It's an online asian grocery store that delivers in many cities. They usually stock kumquats, atleast in my area in NJ/NYC they have "Japanese kumquats" available which are meiwa, not nagami which are oval, I've purchased them before. So you can get fresh fruit that route and collect the seeds if it's something you want to try.
You might also see if there are H-marts or 99Ranch supermarkets nearby they sometimes stock meiwa kumquats (also labeled Japanese Kumquat) you will know they are meiwa by the round shape.
These were from the delivery grocery:
bigger ones were from my small potted tree which unfortunately died off this year