Hi,
You did mention it being a blade fuse in your original post,hence the mixup.
Any good electical retail shop should carry most types of fuses.
Regards,
Greg
Need the specifics, if you are talking blade fuses then it must be ATO (standard car fuse) or Maxi (big car fuse).
Have a look here and filter on 50A
https://uk.rs-online.com/web/c/fuses-sockets-circuit-breakers/fuses/automotive-fuses/?applied-dimensions=4294853291