One of the Oxford papers did an article where they locked up bikes around the city then sent a journalist to go and "steal" them. I seem to remember he was only challenged once and still managed to get away with it.*
It may be worth contacting the broken spoke bike co-op, they may have some knowledge of what happens to abandoned bikes in Oxford. The old Oxford Cycle Workshop refurbished abandoned bikes at one time.
*Not encouraging anyone to steal, article was on the internet so probably not true, etc etc
I know that OCW used to get all the bikes that ended up at the Oxford tip. They were all locked in a cage there. Very inhumane.
Don't know if the abandoned bikes end up at the tip, or elsewhere. If it's the tip, then you might be lucky: I nearly got hold of a Raleigh Twenty that was in the cage until the guy I asked about it double checked with his boss, who knew about the OCW arrangement. Shame.
I don't suppose this is of much use to your query. I'll go now.