I couldn't find any indication in his letters or biography that he had ever returned to Bloemfontein. In a letter to his son, Christopher he writes:
I was much amused by your account of your journeyto Jo'burg on Maundy Thursday....If you fetch up at Bloemfontein I shall wonder if the if the little old stone bank-house (Bank of South Africa) where I was born is still standing. And I wonder if my Father's grave is there still. I have never done anything about it, but I believe my mother has a stone-cross put up or sent out. (A.R. Tolkien died in 1896). If not it will be lost now, prob., unless there are any records....
This letter was written in 1944, so I assume up to that time he had not returned.
Then in Carpenter's biography, p44 (HarperCollns Paperback edition ):
..end of January1921 Caape Town offered him the post. In many ways he would have liked to accept. It would have meant a return to the land of his birth, and he always wanted to see South Arica again.
It is always possible that he may have visited Bloemfontein in his later years, but I somehow doubt it.
I highly reccommend the book 'Tolkein' by Humphrey Carpenter.
Very good advice, Samwisegamgee. It is a very interesting book. I also recommend JRR Tolkien: Artist and Illustrator by Wayne Hammond and Christine Skull, as well as, The Inkings by Carpenter.