Here's what I did to pair up my Clarkii who had been alone for almost 2 years:
I added 2 VERY small juvi's to the tank. Because a larger female has a tendency to be a bit of a bully, that allowed her to beat up on one of them, and end up accepting the other as her mate by default. If you are able to find some small ones it may be worth your money to try this. Instead of trying one, then having her kill it, then trying another. Do them both at the same time and you might have more success.