You can certainly buy both.
The RHS have a good page of advice about growing meadows, that covers a lot of points that you need to know about:
http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=436
We saw instant wildflower turf demonstrated on one of the TV gardening programs earlier this year (I've forgotten exactly which one). It's brilliant stuff. To create a very small mini-meadow, of a few square metres, in a typical garden, it would be economical and ideal. Though it would be too expensive too turf a large area in the same way, IMO.
By sowing seed the cost is typically £20 for 15 square meters (that's roughly a 4x4 metre square). The cost could be less.
Meadow turf is around £10-£20 per square metre. Turf is a lot more expensive, but more reliable.
Many garden centres sell rolls of (plain) turf. But I've never seen meadow turf on sale there. I'm sure there would be demand it they did stock it. I'd buy a roll, if only just to try it.
