David you should be able to buy tickets at the station ok - we ve never had to queue for anything more than 10 mins normally for tickets at any of the polish stations we ve been to
A contact for you is jeffery dobeck at pol rail who is extremely helpful( i think his email details are elsewhere on this forum) - my polish is not great but "poprosze 1 biletow w pierwszej klasie do leszna" is 1 return ticket for leszno please first class
The station in leszno is around a 30 min walk away but there are usually taxis outside the station and i wouldnt think it would cost much as its only a 5 min drive away from the track and you should be able to buy tickets for the meeting at the track
Hope this info helps a bit - enjoy leszno its a lovely place with a great speedway stadium