Checking that a necessary item has been purchased

Is there a way to link two (or more) products such that if you purchase something from product group 1 you must also purchase something from product group 2?

I want to sell shirt designs and blank shirts off my website - so if a person buys a design I want to ensure they've bought a shirt to go with it.
The only way I know of would be to have all the possible designs as a dropdown selection box when they purchase a shirt. If I end up with say 500 designs though that's not a feasable solution.

So can you link the purchase of one product to the purchase of another?

Thanks!

There is nothing built into Zen Cart, at this time, to manage this ...

I am not sure if there are any Add Ons for "have to buy this with this" or not ... :unsure:

I couldn't find any - I was hoping someone on here might have some ideas or know of a module I couldn't find!