I have never heard of anything like that ever happening and to be honest I don't even think it's a crime to sell them. Then again; I can't guarantee the opposite!
Do ask the concierge at the hotel, who might be able to help.
Normal black cab to SW19 from Central London might run you £25 or so - just a guess though. I would, however, just advise you to just call and order a car from Addison Lee (the biggest car/taxi service provider, they give you a quote and are usually very good. 0844 800 66 77.
Just FYI, even if your friend doesn't like it; District line (the "green line" on the tube map) runs directly down to Wimbledon.
Further, I just did a quick search for wimbledon tickets on gumtree.com (UK's CraigsList):
http://www.gumtree.com/cgi-bin/list_...gdom&ubercat=1
Also, here is a ticket seller... looks pricy though:
http://www.accesstickets.com/event-7...FSEulAodCy4SQw
Lastly, most pubs show Wimbledon and I personally often watch the matches at Bluebird Cafe on the Kings Road. They show matches on a big screen in the outdoor seating area. Great for a boozy lunch if the weather permits.
http://www.danddlondon.com/restaurants/bluebird/homehttp://www.wimbledonatbluebird.com/