yose, you’re correct, it isn’t easy. A kesher isn’t something that comes instantly. It can take years to form a real kesher.
Part of mourning is realizing what we’ve lost. We are supposed to mourn for a Rebbe muvhak just like for a relative – we tear keriyah for it! Just like you can’t replace a parent, you can’t replace a Rebbe.
I think gavra had some good advice. A talmid from the same rebbe as your rebbe would be a good idea, or a talmid muvhak of your rebbe.
Hatzlochah!