Quite a few options on amazon for shorter pieces but I can't find any that would be suitable for a long stretch bordering a room. I'm planning on using this for a door threshold though:

https://www.amazon.com/Precision-Metals-9736-Thickness-Length/dp/B0006N6JO2/ref=dp_prsubs_1?pd_rd_w=P8ASG&content-id=amzn1.sym.ec3cee7c-6bd8-496a-8166-4fdb6d51cad1&pf_rd_p=ec3cee7c-6bd8-496a-8166-4fdb6d51cad1&pf_rd_r=D43B1E9S1KWA5QFH8EP2&pd_rd_wg=zHWu7&pd_rd_r=5f75fa14-51a0-452c-9d22-c635b335545d&pd_rd_i=B0006N6JO2&psc=1