As Bruce mentioned, the MBB series turned into the AGC series a long long time ago. The AGC is a 1/4" by 1-1/4 glass fast blow fuse. So what you are after is a Bussman or Eaton AGC 1/4A fuse.
Here is a link to a page where the fuse types are discussed and the mention made of the MBB type.
https://www.galco.com/techdoc/buss/mbo-8_dat.pdf
Here is a link to the specific fuse on quesiton, but you will likely find them locally. They are not rare.
https://www.allfuses.com/agc-1-4