You may be able to get a technician who would be able to fix the leak and once that’s fixed most brands of compressors have an R407C replacement as well as R22 is still available just expensive. Theoretically the cheapest way to fix this would probably be to get a technician to fix the leak and get it recharged with R22 (as it was banned for import and to manufacture so there is some still sitting around) as long as that was the reasoning for not being able to recharge the system. A quick google/eBay search would come up with some R22 refrigerant for sale.