The DOS versions are collector items, the Windows version was available in the year 2001 at the "Chips & Bits" shop where I bought it. They don't have anymore the popular bundle with "Roller Coaster Tycoon" and "Railroad Tycoon". (status at 13 Nov. 2001). Another place to look is Amazon.co.uk
Look below for Tansport Tycoon on Ebay. They have often 10 to 20 offers of Transport Tycoon games.