I see trailer tires and rims sold at places like Farm & Fleet and/or Rural King but I really only need new tires.  Is it "better" or cheaper to have new tires placed on the existing rims?  Do most tire stores carry trailer tires?

It should be cheaper to just buy the tires themselves. Ask someone about it at farm and fleet and I'm sure they can give you prices to compare.

The local tire shops here carry trailer tires. 

I found that trailer tires come in different ratings. I don't recall off the top of my head what they are but make sure the tires you choose meet your weight and speed application. Cheaper isn't always better. Whatever you do do not put a regular tire on a trailer. The side walls aren't strong enough for the long haul... heh. 

A follow up question.  My tires have been scalloping a bit (hence the need for new tires) and I'd rather not repeat this on new tires.  Does anyone know what would cause this on a trailer?

Places like Eastern Marine Trailer Super Store carry them but if you look I bet you have a tire center, West Marine, or local trailer parts store. Check the price on other places on the internet as well.  Just remember if you buy the tires you still need to find a local shop to install them. Both of my local trailer parts places will sell and install them as well.  For bigger 14 or 15 inch tires you may also want then balanced. I hear it makes a difference. 

On 8/10/2016 at 1:30 PM, Ratherbfishing said:

A follow up question.  My tires have been scalloping a bit (hence the need for new tires) and I'd rather not repeat this on new tires.  Does anyone know what would cause this on a trailer?

The same things that cause the problem on car and truck tires: misalignment, incorrect pressure...