They do carry Masonite. They just are not called Masonite. I just ordered doors from Lowes. The outer theater door is a 1-3/4" Palazzo and the inner door will be a 1-3/4" solid core door from Menards with green glue and MDF. Lowes sub-contracts the assembly of the door. In our area their first choice is Reliabuilt who buys the slabs from Masonite and assembles them.Even Lowes has the Palazzo on display and its called Palazzo. But for my 1-3/4" door they went through a different supplier to assemble the door frame, but it is still a Palazzo door slab. The vendor of the custom door was Badger something, something.
It is painful working with Lowes, but we got it done. I wanted to buy through the local small hardware store who specializes in doors and windows, but WAF thought Lowes would be cheaper (no quote to confirm). One employee at Lowes said the special order 1-3/4" door would cost over $100 more. No deal. But when we went to the store, the computer only said $70 more and we got a discount of $100 because we spent $1000 on doors for the basement, so it was a wash, and we ordered the door.
There used to be a lot of talk about Safe-n-Sound when it first came out. I think the consensus they were not so "sound" for our application at least. I could not test how heavy the door was, but I have no illusion of it being as heavy or as "sound proof" as my solid stave inner door slab (just $50 too)...just prettier. STC is listed in low 30s but that does not take into account low frequency performance.
Lowes also has full MDF doors too.