Of all the fruit trees I have purchased, I have never heard of a GMO fruit tree. As stated above, there are none on the market. Fruit trees are grafted using root stock and scion from the cultivar desired. this is a mechanical process not a genetic modification. In ancient times a seed may have produced a clone of the desired tree, but not any more. Most fruits are the product of hybridization and crossing and will not come true to variety.
The goodness or badness of GMO plants is for another, very protracted and divisive discussion, but as for purchasing fruit trees, buy away and stop fretting about getting a GMO product.
If you want an area tree seller, search for a reputable nursery near you. I buy mine on line from https://www.starkbros.com
with never a complaint or problem.