BB, Join the LAA in the back of the magazine is asection in the classifieds titalled shares for sale.
Also get down to your local airfields or better yet strips. There will be a notice board with shares for offer.
Join your local strut, go to the meetings you'll soon find plenty of people who are looking for shareholders.
Most private pilots will struggle to get good utilisation of there aircraft so shares makes sense as the finacial burden is spread and the use goes up.
A slightly risky stratgy is to buy an aircraft yourself and then sell shares in it to recoup most of your costs.
Oh and I doubt you'll get much of a share in an RV4 for £10K. Think Jodel, condor, RANS S6 or similar.