Hi,
If your looking for not conduit tubing I used m-machine-metals they are a bit old fashioned in that you have to order by email and pay over the phone, but the prices are pretty good, they should have stock of both 25 & 25.4mm 316/304 SS and seamless tube.
No affiliation, but have used them many times for my mpcnc build and general metal supplies and are always pretty good.