Bearing #6808 has same OD 52mm as the one needed, but ID is 40mm. The width is 7mm. Two of them can be used on the machined bushing 32mm ID and 40mm OD with 4mm shoulder. I'm not sure how long these are going to last, but 6808 is available cheap and maybe worth a try.
http://nobtech-hosting.com/cgi-bin/secure_html/bearingsdirect/autocart.cgi?CAT=12