Have a look around for Warcraft 2: Battle.net Edition, which includes both Warcraft 2: The Tides of Darkness and the the expansion set, Beyond The Dark Portal.
I've checked a few of the popular UK e-tailors and most either don't list it anymore or are out of stock (War2:BNE was released circa 2001 IIRC). However, there are plenty of secondhand copies about, so an auction site or the member's market would likely suffice for both War2:BNE and Warcraft 1: Orcs & Humans. Alternatively, you might still find a new and sealed copy in the budget section of larger brick and mortar retailers.
Cheers,
BrynS