You want what is known as fuel filler hose. Most auto parts stores should be able to get it for you and some will have it in stock. Maybe not the local Discount Auto outlet, but surely a NAPA auto parts store would have it. Marine and farm supply places also usually carry it. It comes in several diameters (bores), so make sure you know the size you need when you inquire.
Some factory fuel filler hoses come pre-formed to make relatively sharp bends. Look at your old one and make sure it's not one of those, 'cause regular flexible fuel hose may kink instead of bending when trying to make those turns.
I had to replace the same on our RV afew years back. Ours even had a metal stiffening spring inside of it. I ended up getting a section of a rubber exhaust rubber hose from a marine parts store. The hose is used for fuel and exhaust applications and comes in many large sizes. It is sold by the foot. It has been in place for several years and continues to work well. You will want to use a good sealer (RTV silicone style) to use with it, as the rubber is too stiff to be properly sealed with just a clamp.
There are online sources as well - just Google "fuel filler hose" or "fuel delivery hose". You need a softwall hose to bend it in one piece or straight hose coupled to 45 elbows to make a multi-piece hose.