Cornwall has a strong native pony tradition and a close-knit equestrian community where reputation matters. Shetlands, Dartmoors, Welsh sections and native crosses are all readily found, and because word travels fast locally, sellers tend to be straightforward about a pony's quirks — nobody wants a reputation for selling a difficult pony to a family two villages away.
The practical consideration is geography. Cornwall is long and narrow, and a pony near Bude is a very different journey from one near Penzance. Factor in the drive, and be realistic about transport costs if you are buying from outside the county. Coastal grazing can be exposed and salt-laden, and many Cornish ponies live out year-round — which usually makes for a hardy, easy-to-keep pony, but ask how the pony has been managed if you plan to stable and rug through winter.