There does not appear to be one, or at least I haven't found one yet.
There does not appear to be any provision for it in the eBay Find API documentation, which means it probably doesn't exist in the web interface search either.
Been pondering whether there would be any reason for eBay to have a managed payments filter since it is going to be the default payment method -understanding the reasoning behind that could be helpful in determining if there is any good reason for eBay to code in a MP filter, and if there isn't, reinforces the probability of there not being one hidden somewhere.
