If you supplied a link to another website that gave flash cards that were cohesive with the website here for the courses here, but from another entity or company, you wouldn't loose (hopefully) your non-profit status due to it not being you that was making the money from this.  Also IF it is allowed to own two companies that are separate from each other and sell the flash cards then go for it just make sure you read up with a lawyer or something to make sure its all legal but you could make a lot of money selling flash cards I know people have been asking for them.