The nearest station would be Oldham Werneth which will be closed for the game, so buy your ticket to Manchester Piccadilly and take a bus from the station.
Services operate every 15 minutes or so on Saturday afternoon. Numbers 24, 181 & 182 make the 25 minute trip to Oldham and will take you to Boundary Park.
The 181 goes right past the Rifle Range pub, top recommendation in the S24 'Pub Crawl', and a short 10-minute walk to the ground.
To find the latest service information including the present costs go here: www.nationalexpresseastcoast.com