How recent does "contemporary" mean? It sometimes means living composers, it sometimes means anything written after 1900, and it could mean anything in between. Is there a guideline? Typically if a competition is asking for something that doesn't have immediately obvious options, it would provide some suggestions. You should also ask Thomas's teacher.

If music from more than 50 years ago is OK, then consider this anthology, which you can order from the website:

https://www.violinmusicbywomen.....tents.html

The Intermediate 1 volume and maybe the first half of the Intermediate 2 volume would be appropriate based on what Thomas has been learning recently.

Unfortunately, I don't know of anything more recent that Thomas would be able to play -- virtually everything I know of by living composers is professional repertoire, though I'm sure easier pieces exist.

The anthology I linked does include some music by living composers, but the easiest piece in it that's by a living composer is the very last piece in the Intermediate 2 book, which according to the book description requires 6th position.

I think it would be a good idea to seek clarification on "contemporary," because if the entire 20th century is allowed, the vast majority of the pieces in that anthology become options.

Here's a piece that also might work:

https://imslp.org/wiki/Adorati....._Florence)

If you click on the "arrangements and transcriptions" tab, you can find a version for violin and piano. It's about three and a half minutes long. Doesn't go very high, but definitely requires third position because it contains double-stops that are not playable in first position. Some of the double stops would be difficult at Thomas's current level (especially legato thirds), which is why I still hesitate a little to recommend it.