A good place to try is a fashion college. London is the place for this, for sure. I know for a fact that some impoverished student would be only too happy to use their skills and resources at their disposal, to knock something up for you, for some rent/beer/food money. I think professional dressmakers tend to work to tried and tested formulae, but are another option. Getting a clothing manufacturer will be difficult; they don't want you stealing their market. you could try approaching some, but be prepared for them to offer next to **** all for your designs (they know you lack the resources to realise your ideas, so have that power).
To succeed, I'd reckon you'll need a USP, and have something quite different/distinct from other stuff that's out there. Think Rapha, Ana Nichoola, that sort of thing.
Gonna cost yer. No way round that.