TL;DR, you can try SRAM wide cranks if you need gravel sized chainrings. Funny BB systems but readily available everywhere. Can be used with normal chains.
Some BB386 cranks may work too
surly steamrollers should take more that 48t, I ride one with 49t , 8bar track cranks with HT2 bb (I believe these are rebranded andel or something something taiwan) and there's plenty of space left. hope the pic helps a little
edit:sorry its just a 46t in the picture
TL;DR, you can try SRAM wide cranks if you need gravel sized chainrings. Funny BB systems but readily available everywhere. Can be used with normal chains.
Some BB386 cranks may work too