13-in rolls are pretty hard to find, most of the 3rd party papers only come in 17" or larger. Additionally, if the R3000 is like my old R2400, it only support 2" diameter roll cores; which means you still have a problem if you cut down a 17" roll, since most of them are on 3" cores. It's possible to cut down a 17" roll and then rig up some sort of roll feed behind the printer that can handle the 3" roll cores, but it's pretty clunky (not to mention the money wasted throwing away 20% of what you buy).
For RC papers, Epson does make their premium luster and premium glossy papers in 13" rolls with 2" cores. I've used the premium luster 13" rolls in the past, and as far as RC-luster papers it's one of the best. The only thing to be aware of is that it comes off the roll with pretty heavy curl due to the 2" core and the nature of the paper.