Sure, you can contact them but it doesn't mean they have to talk to you. It would be better if the executor or personal representative for the estate initiated a will search. If the estate is represented by an attorney then let that attorney take the lead. Some attorneys are part of listserves or can post entries in other trade journals. Usually the quickest way to find a will.
Reading between the lines it sounds like you either have a specific lead on an attorney that produced the will or you are concerned that the estate is not all that interested in find the new will. So have at it and see what happens.
It's not clear from your question whether the testator -- the person who hired the dead lawyer to write his will -- has died. If he has, and if the old will has been filed with the Probate Court but NOT yet allowed, you could challenge the will on the grounds that there is a newer will out there. The person who is seeking appointment as executor of the estate would then be forced to prove that there is no newer document.
If this is the case, keep in mind that challenging the validity of a will is pretty technical stuff, and you'd be well advised to hire an experienced probate attorney to assist you.
Thanks for this interesting question. The search for the true "last will and testament" is a classic search for the truth. Just because a will shows up in an attorney's files doesn't mean that it is in fact the decedent's last will. Only by carefully--perhaps even diplomatically--inquiring of family members will you be able to piece together the factual "fabric" necessary to at least create a question as to whether there was in fact a more recent will. One thing to keep in mind is the attorney who the decedent would have engaged to prepare a later will, and/or the family members who would have been nominated by the will as executor or executrix. Persons or even charities who you believe would have benefited from the later will might have reason to know of an amendment.
If and when you have additional facts to call into question whether the will asserted to be valid truly is valid, you should then engage an attorney to dig more deeply and make it uncomfortable for those persons who may be trying to defraud the Probate Court and potential heirs by misrepresenting the state of the decedent's will.