What I meant is that this is a use case where such a public function would be handy.
Actually, if I understand the problem correctly, I don't think it's necessary. I think this should work:
char buf[MAXPDSTRING];
sprintf(buf, "_my_external_lib1234_%s", s->s_name);
if (buf->s_thing)
t_send_test* sender = (t_send_test*)buf->s_thing;
Then in the pd_bind call for the sender, just make sure to use the same prefix "_my_external_lib1234_" on the front of the symbol.
class_getname is already a public function, so you can even use that to error-check for the edge-case where someone else tried to bind to that same name.
-Jonathan