Could be you’re right, but I’m pretty sure there’s no Beis Din in Lakewood that does geirus under the auspices of R’ Nissan Karelitz. There is one that used to work with R’ Nochum Eisenstein, but I’m not sure if that is still the case.
There is an organization called Tiferes Bais Yisrael that helps direct converts to Batei Din that are accepted worldwide, and also helps in finding mentors and rabbis that will help along the way. They have a searchable database on their website: jewishfamilyfocus-dot-org.
Good Luck