Looks like MHSRV has a 27B:
https://www.mhsrv.com/2019-thor-moto...-a-tx-i2187769
They are one of the better dealers in the nation. (In fact it may be better to pay their price than find a cheap one across the country.)
If you're planning on buying elsewhere due to price you could always contact a local dealer and see if they will perform your warranty work for you (the answer most likely would be "no" but you could always ask). You can also contact Thor and find a local repair shop that can do the work for you.
Another option for repairs (albeit a long drive for you) is factory service in Wakarusa, IN. You'll find no better shop in the US than factory service to fix a Thor.