Glasgow and Strathclyde is west-central Scotland's most populous and urban area, and — much like Greater Manchester or the West Midlands — genuine grazing within the city itself is limited, with most families looking to Ayrshire, Lanarkshire or Stirlingshire at the fringes for an actual pony to keep. The scale of the population supports an extensive riding school and Pony Club network for those without land of their own.
Good motorway links radiating out from Glasgow make widening a search genuinely practical — Ayrshire to the south-west, Lanarkshire's Clyde valley to the south-east, and the Trossachs fringe to the north are all realistic day trips. Expect city-adjacent prices for anything kept close to the conurbation, easing considerably the further out into Strathclyde's wider countryside you are willing to look.