I've never heard of an open-source lawyer. I understand totally how valuable it is to litigate open-source issues, but I'm curious as to who pays for such services? Being able to pay lawyers seems unlikely for a free product.
10 out of 10 of the largest tech firms in the world release significant opensource software: Microsoft, Apple, Amazon, Google, Facebook, Alibaba, Intel, Oracle, Samsung and Baidu. They turnover more then $1 trillion and use many lawyers.
Any company that either uses open source code or releases open source code needs competent advice. Asking for such advice from a lawyer unfamiliar with open source is probably pretty expensive.
As real world application of open source licenses is rather complex (I would say: A nightmare) you definitely should consult a lawyer if you want to put sth. Open Source. Btw. it gets even more complex if you think about application under local laws of multiple countries.