Hum... UCD cycles every time a track is loaded. So racing is out of question.
You'll have to use the dupe glitch or the birthaday exploit in order to get some cars and the sell them. I think that way you will earn money without losing the chance to buy that car.
If you don't want to use that you could ask for cars in market place and then sell them, or just ask for the car you are looking for.
Otherwise you will just have to wait that car to appear again.
Hope it helped
Sorry for the thread hijack, but is tha an A-series Manta in your avatar? I had a C GT/E Coupe for years.
Birthday gift yourself a bunch of Ferrari F40's.