Firstly, unless your aunt has a queue of people waiting for her breeding females, you won't be harming the breed by having a few and not breeding them pure (except when/if you have the opportunity.)
I often think that the 'must breed pure or you're harming the breed' mantra causes more harm than it does good - a lot of people don't take on rare breed females for that very reason, but as far as I know, most breeders do not have waiting lists.
It seems to me that the more people want to buy rare breed females,
for whatever reason, the more can be bred, which can only do the breed good, surely?
(There are a few breeds where this is not true, or is less true - Shetland cattle, for instance, make such good crosses they nearly lost the breed, so there is a lot of sensitivity there.)
There is a flock of Manxes near Castle Douglas - not very close to you, I know, but a little nearer than other options. And there is a network of people who are happy to help transport / harbour rare breed animals en route to breeding homes (our own Fleecewife being one such), so an occasional registered aged tup, or tup lamb, could probably be arranged...
Oh, and transferring one at the Scottish Smallholder Show would probably suit most smallholders, eh? Then there's Lanark Rare Breeds Sale end August, Carlisle Rare Breeds late Sept...
Again, because I love them, I'd get some in-lamb ewes from your aunt, and take any opportunity to breed them pure when it arises but be happy to put them to a nearby small/easy-lambing commercial tup (or a Shetland or other primitive - there will be some around you could borrow or take the girls to) when you haven't sourced a Manx.
However, if you really just want a few sheep, and Manxes don't especially float your boat, then it'd probably be easier all round to just get a few commercial types from your local friendly farmer. You shouldn't feel bad about taking that option if it suits you better.