Originally Posted by MarkWW

Doing some researching, this is the best advice I can give:

Outboard BB cranks are available for MTB, road and track cranks. 47T chainrings seem to only be available in 110, 130 and 144 bcd, which means no MTB crank would work short of getting some kind of custom ring. Track cranks are generally 42-45mm chainline, so skip that. Road double cranks are 43.5mm chainline, so that leaves out standard road cranks and compact doubles. This leaves 130bcd road triple cranks. Looking at some shimano techdocs, a tiagra OBB triple crank has a 45mm chainline to the middle ring. Generally rings are 5mm apart, so in theory, putting your 47T chainring on the outside of a road triple could potentially give you a 50ish mm chainline. Problem is, this depends on chainring thickness and tooth offset. I don't have any information on that. Hope this helps.

tl;dr: try a road triple.