It would be extremely unusual for a solicitor or counsel to take on a will dispute on a no win no fee basis. Although you might manage it on a good Inheritance (Provision for Family and Dependants) Act 1975 claim. The problem with will disputes is, by and large, the best witness is always dead so you have an evidential difficulty from the off.
You should try contacting the Law Society Probate Section, STEP or ACTAPS for a list of solicitors in your area. They may provide details of no win no fee firms, if indeed there are any.