well, they could have thought you meant Multigrade Rapid--which I think was discontinued within the past year or so. MG Rapid was a developer incorporated multigrade paper--very similar to MGIII, but made for use in certain machine processors like kodak royalprint.
To me-- "MGR--1M, 5x7 250" means Multigrade rapid, RC (m= medium weight), 250 sheets of 5x7 in Ilford packaging lingo...I may have an old box around the lab someplace, but I used to use MG rapid alot. Good paper--had some lousy longevity issues though.
it could very well be that the replacement would be Ilfospeed Deluxe though-- a graded RC paper used in alot of machine processing as well.
I dunno--wild guess.