I have the same crank on my 1974 Raleigh Competition. I believe it has a 42t inner so you may be able to tease one out of the ebay market. Personally, I'd recommend using that 52/48 to set up your bike with half-step gearing. Assuming it's going on a 5-6 speed vintage bike, half-step will be perfect to reduce the number of duplicate gears.