Sign comp makes one.Also eastern metal supply in florida has them to.
We don't use either of those raceways now a days.
They are costly,usually 8",come only 24' and are heavy.
Don't need the extrusions that are designed to hold neon transformers any more.
Raceways with led power supplies can be 2" thick
1" if you place the power supplies behind the wall.
We do this now.
fold up a 040 u to mount the letters on.
fold up a matching u to go on the wall.
cap the ends.
Makes the install go easier too.