At least in Michigan, the primary ballots pretty much list the actual candidates.
A few times, when things looked murkier, I've just contacted the local (city or county) party organization, and quickly gotten answers.
If that didn't work, I'd probably try contacting the League of Women Voters, County Clerk's office, or similar [non-]governmental groups that work at keeping track of such things. And some web searches, looking for primary candidates with on-line campaign info.
A few times, when things looked murkier, I've just contacted the local (city or county) party organization, and quickly gotten answers.
If that didn't work, I'd probably try contacting the League of Women Voters, County Clerk's office, or similar [non-]governmental groups that work at keeping track of such things. And some web searches, looking for primary candidates with on-line campaign info.