It is pretty simple. When one is serious about successful spawning and subsequent raising of fry, in most cases this requires a species tank. I say most because some fish spawn and depossit there eggs with those of another species to beraised by that other species' parent(s).
With most bettas you need to separate the parents after a successful spawn. The only bettas I have spawned were imbellis. However, I also spawned one mouth brooding cichlid- P. nicholsi. But the mom held the eggs until they were free swimming and let them out. The male had to be removed as soon as she was holding because he harassed her all the time.
The first spawn was a success and mom spit a nice brood of young and I was quite happy. 36 hours later there were no fry left- she ate them all. So the next time I stripped her when she was close to spitting and put the fry in the tank and she went elsewhere. I did this by netting her and while in the net in a bucket of water I raised her to be partly above the surface and she began spitting. I lowered the net and then maneuvered to to release the fry into the bucket. I then raised her again and she spit some more. I got alll the fry out that way.
I managed to grow out the fry. When I had reunited the mom and dad after the first spawn, he killed her and had to grow out a dayghter to get another spawn. Ultimately I sold some of the kids and then gave the rest and the parents away to a friend.
The point is, breed your fish in a dedicated tank. Be able to remove one parent after a spawn. Be prepared to remove the other when the fry are spit.
As for finding the needed male, and getting better info than I can offer, have you tried the IBC?
I know nothing about these guys but they are in CA. The have what you want in stock: https://bwaquatics.com/products/6qkuko5edszpeouygearvg6ca9e5y1
They also have imbellis.