Here's the address of the RHS list of plants with that name. I took a quick look at some, and they had an added name - a surname - but I did see a Dianthus and a Fuchsia with just 'Thomas' as their name. As there are so many, I didn't check them all. I'll leave that to you. I'm afraid that all the roses have additional names.

Copy and paste this into your browser.

http://apps.rhs.org.uk/rhsplantfinder/pfgenera.asp?txtName=Thomas&page=1

I hope you find something suitable. I have a hardy geranium called 'Memories' for my Mum.

There is a site "Country Garden Roses" where you can name your own rose.