Please offer specificity with these kinds of requests. Star Lord wears multiple different coats in the film (the trench, the short jacket, the uniform jacket for the end).
A quick search on Google of "Star Lord Jacket" brings up the following links on the first page (these are for the short jacket he wears for most of the film).
Etsy
The Jacket Maker
If you are looking for 100% screen accuracy, you are probably going to have to commission something (which will be expensive). But a few things there would offer at least a good base for you to start modifying.
There's also the
"Definitive Peter Quill/Star Lord Thread" here on the first page, I'm sure there's something usable in there.