Check out these threads:
viewtopic.php?t=19439
viewtopic.php?t=45921
It ended suddenly and people stopped responding, but it does have some useful tips in it. Also, check out this forum:
http://www.anafricangrey.ca/forum
Warning: When I first joined that forum, the members were a tad rude when I said I was looking for breeding tips. When you post that you're looking for tips, people assume you're not experienced and that you are just jumping into it. I have to work to get them to understand that I've been breeding for a while and I have the experience. So don't take it personally, some "old school" breeders are just that way.
Just wait it out. I have my pair for 6 months before they started working the box and now I've had them almost a year and they are still working the box. Greys are one of the most finicky species and it takes a lot of work and a lot of patience, ust like with all other species. Make sure you are giving them plenty of full-spectrum lighting (Light bulb CRI above 80). It's hard being so far North, but you can get light fixtures and sunlight bulbs to help.
Lots of fresh, warm foods. Beans, rice, bread, sprouts, veggies, hard boiled eggs, etc. Try feeding this more that the pellets. You could even add a calcium and vitamin d supplement. Try Calcium Care by Phoenix Unlimited. Vitamin E is good, but its mostly used for skin nad feather care.
Grey breeding season begins roughly in February of each year and last through early spring. Some breeders are lucky and have two clutches a year. They like being around other African species, such as other greys and poicephalus. That's why many people who breed greys breed only Africans.
Good Luck!