You must need a "boot" for a single disc drill?
What is the drill model?
What is the number on the casting?
Hard Iron bearing or ball bearing? (newer than 1961 or older)
Short or long? (drag bars for each disc alternate between short and long)
LH or RH? (side of the boot the disc mounts to)
The drill you have MAY be similar to the model B in the .pdf parts catalog at the link below, from which you cold post a part number (if different from the number on your casting).