When I search the NCI Clinical Trials, set Cancer Type/Condition to "Myelodysplastic/myeloproliferative diseases", and set Stage/Subtype to "myelodysplastic/myeloproliferative neoplasm, unclassifiable" I find 4 trials. None of them are specifically for MPN-UC but they each list hospitals or research centers.
I don't know of particular centers in the U.S. that are known for treating MPN-UC but there are many excellent centers for the various types of bone marrow failure diseases. Depending on how you measure them, M.D. Anderson is definitely one of the top U.S. treatment centers for cancer in general.
Here is one report ranking them #1. If your brother can come to the U.S. for treatment he should go to a center that's on the list of
comprehensive cancer centers as determined by the National Cancer Institute.
Have they searched for a matching stem cell transplant donor yet? If he's going to get a transplant then your criteria for finding a treatment center probably changes, because if he's getting drug treatments then you want a doctor who knows a lot about his disease while if he's getting a transplant then he'll want one of the best transplant centers, which are generally the centers that do a lot of transplants.
Here is information about selecting a transplant center. The statistics and lists are for U.S. centers but the same guidelines apply in India.