i think i have tried a lot of the combos to get a tilia flower...but i'm throwing in the towel. can anyone tell me what will work?

It would have been better to post your question in this thread but still... the tilia flower is one of the rare tier 4 types. Tier 4 types cannot be cros-bred which explains why no combination works. To get these types of flowers and foliages, you will need to either buy the most expensive seeds in the shop or use the mutation liquid on your plants. Both of which will also require luck.

"Tier 4 types cannot be cross-bred" except by Tier 4 plants! When you have 2 or 3 of them you may cross-bred them!!