I have those lights on the bus. Yours actually look pretty good compared to mine! I've spend some time trying to find parts, but no luck. I concluded the bases would need to be fabricated.
Good luck with them. I do like them and they are still on the bus. I do have some spares that I've collected, but again, the bases are needed.

~ Victor
1941 3/4-Ton Pickup (in process). Read about it in the DITY Gallery
1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD
1957 3100 - moved on
1959 C4500 Short Bus "Magic Bus" - moved on
1959 G3800 1 Ton Dually "Chief" - moved on
1958 C4400 Viking "Thor" ~ moved on to fellow Bolter