When breed "Het Russo" together then you also have 25% chance to get BEL as well.
Same thing with "Mocha", its super form is "Latte" which is another BEL.
So what make BEL are Lesser, Butter, Mojave, Het Russo, Mocha. However, each morph produce different % white BEL though.

Imo, it seems easy to get BEL, however they're still expensive. I think I'll wait lol