The butyl tape I used is pretty standard. I bought a roll of it for about $11 on
Amazon.
Camping world (or many RV dealers) will stock tubes of Dicor. They may not have the exact color of the OEM Dicor though. White and tan are pretty common colors.
Remember, set aside at least 2 hours to get off the old sealant and tape after you remove the old vent cover. Plastic blunt putty knives helped. But rolling it off with your finger tips was the least risky method of preventing rupture of the roof membrane.
Good luck. Let us know how it goes.