What are you looking for? To buy, tune, ...?
You can buy antennas online, 50Ω coax is also online. Radio Shack sells both but they dropped the 102" whips a while ago. Soberbyker is probably more up to date as far as hands-on with the present generation of radios & antennas.
RG8U is bigger, like about 10mm. For 4-5 watts @ 10 meters (CB band), you should be able to get away with RG-8X (dia= 1/4") or 58U (0.195"). Unless it's a long run or you might be
diplexing a higher frequency into the same line, the smaller stuff should be okay.
The biggest challenge you'll face is waterproofing the PL259/SO239 connection at the antenna.
PM me if you need tuning.