2 things that could get them to breed....
1) don't do a water change for a while about 3 weeks and feed them a little bit extra like once a day more food... then after about 3 weeks, do heavy water changes I would say the first 75%. with cool water, (Say tank is 80-82, use 76.) then do 50%, this way it tricks them into thinking it just rained out, and encourages them to spawn, sometimes..
2) do 50% water changes everyday, and make sure that gravel (if you have any ) as clean as can be.. when you doing those water changes keep cleaning that gravel, for me i don't use it, because even when you think it's clean it's not... but some fish have to have it to breed on... I bet in about a week or so you should get them spawning again...
also if the fish are big enough,,, feed them night crawlers... (cleaned out) something in the worms gets them going, and also they will lay more eggs..
andy