It's often thought that lawyers are a service, like doctors, and will take any case presented to them, regardless of subject (within their area of expertise).
This is true of neither lawyers nor doctors. In general, neither is under any obligation to accept any client (subject to their employment contract and, for a doctor, an obligation to render first-aid).
That said, most lawyers are not litigators and never go near a court room.
Are there also communities of lawyers who have a specific motivation to influence law or establish precedent? By that I mean lawyers who only accept cases (or even those who aren't accepting cases at all and instead seeking them out on their own) on the merit of being able to argue for a ruling that would either question an existing law, force a ruling (and precedent) on an existing issue, or cause a previous law or ruling to have different guidance established
For example, the ACLU actively seeks these sorts of cases. Similarly, government lawyers will launch or defend cases if they want a precedent set - it’s a fair bet that government lawyers in US states with ostensibly illegal abortion laws will actively be seeking prosecutions which will end up in the Supreme Court.
Of course, lawyers are disproportionately represented among politicians and their staff who’s reason for existence is to influence laws.
Notwithstanding, all lawyers have an ethical obligation to the best interests of their client and to the integrity of the legal system.
Are there conventions or discussion areas so that a layperson can learn what types of issues are important to the legal community?
Or does their bar accreditation require them to provide some sort of access requirement by the public?
Most lawyers are employees and do not take commissions directly. Those that operate a legal business can decide which work to take or not take like any other business.