I don’t think they are available anymore. If I remember correctly another Honda model only had the right side disc. And that created an extra amount of the lefts. Second hand is probably the only option.
VTX1800.
That's my other "other" set(s)...
ETA:
For the smooth set: 55-107R and 55-107L.
For the original ribbed covers: 1-237 (L) and 1-238 (R). I need to check my stash to be sure of the right side number.
FWIW, JC Whitney also sold these around the time the Valkyrie was first out. Additionally, Rivco offered a swept-style set.