Hi Chris
I appologise on behalf of everbody that we have not yet answered your question.
Although I don’t use spray varnish myself I can say that my dear wife does and she finds the "Clear Cote" brand an excellent range of products.
Their spray cans seem to last for ages, they produce a first class and quite duarable finish.
Jane buys hers from Hobbycraft and I have seen them in the local B&Q superstore.
Hope this helps
Paul