I have had very good experience with American Frame in Toledo, Ohio USA.
You can buy supplies to mount your own or have them cut the mats and send the frame parts. In my retirement I take advanced photo courses at U Akron, OH. They require twenty 11x14 prints or larger, matted and over matted per course. Some of these have gone on to have shows requiring frames and glass. My images have ranged from 7x17 contact prints to 20x24”. I have used Nielsen (spell) extruded aluminum frames, though many others are offered. They now offer free shipping on orders exceeding $50.00. They say they will ship frames in two days, but my experience with mats and frames has been that they ship within 24 hours of your order.
A large portion of their business is school related so you are likely to have better service and talk to people that can take more time with you if you avoid the last week before college terms end.
I have also had good experience and buy many other supplies from Hollinger Metal Edge.
Because of bad experience it has been several years since I bought from Light Impressions.