I read that there are Dumaguete Silvanas sold in one of the stalls in Cash and Carry near Cha Time. Also, they say Mrs U's silvanas from the same place are equally as good. House of Silvanas are highly recommended as well. The owners are from Dumaguete according to a forum with the same inquiry as yours. They have scattered stores around manila. There's one in Glorietta 4, Katipunan White Plains, Aurora Hemady St, Edsa Shaw, Eastwood and Alabang to name a few. If you want them delivered to your door steps instead, you can order online from https://www.facebook.com/Silvanas-Dumaguete-Manila-Distributor-1494989554081898/
I've been looking for the same kind here in Manila but I haven't been successful in my search yet. Aside from their Dumaguete branch, they expanded to Cebu. I think we just have to wait for a bit longer but hopefully they'll bring it here too!
I heard that Sans Rival in Cash and Carry isn't there anymore :( but good news is, I believe there are people who do pasabuys of it. I'm not really sure if it's a consistent thing or just one instance.