Firstly, I am sorry to hear about your loss.
I am not really to sure about the documentation side of thing's and how it would all of been stored ect, but I expect that the new solicitor(s) should have been given all documentation when they changed hands. If you have no luck after the current Solicitor has looked for the Will, then try to get hold of the Solicitor who drew up the will, as you have said, you don't need the stress of going to Probate as you are still coming to greiving / term's with your loss and the next couple of week's especially are going to be the toughest. Once again, I'm sorry about your loss as I know how difficult and painful it is. My condolences go out to you and your family.