What enlarger do you have? There are plenty of cheap used 39mm lens boards available for Beseler 45 enlargers. A 150mm lens will need a board with a 50mm hole. It is less common used, but not that hard to find. Both the 39mm and 50mm Beseler boards are available new, but they are pricey.
Note to the OP; the Rodenstock Rodagon 135mm available from B&H comes in a 39mm mount.