Answer

The only place I can think of is in Kilmahog, Callandar - called the Scottish Real Ale Shop.   They sell so many bottled beers that they must have some Kolschⁱ.

beersofeurope.com sell many brands of Kolsch & are the only beers-by-post outfit I can truly recommend.

If you are looking for it on tap then good luck to you!   Maybe finding who imports famous names such as Fruh or Kuppers & asking where they deliver it to might get you somewhere.