I haven't been checking the saucer shop much, so it was pure luck that I decided to try and get some new monsters when I did.
The saucer shop in the second town, the three-level factory thing, had a PieRipper!
I've been told those come from the Pirates of the Caribbean DVD, and it is definitely a ??? subtype.

I'm not sure how I could prove it - I still have the saucer, although I had him engrave it as 'Lucky', and could take a picture of the saucer section, but I didn't think to get a picture of the shop with the saucer in it.

Yeah I see rares at the shop from time to time... apparently certain "rares" are a little less difficult to get.

Not only can you get disks in the shop, I've gotten "Book Cards" from killing enemies. Gotten 4 so far, 2 of which were new monsters for me!!!

This game is much more friendly to the ranchers with few discs....

So far I got the Book Card for Pancho/Jell and Golem/Golem. I had already shrined a Pancho/Jell but not a Golem/Golem so I was happy to get one. :D

What are the Book Cards for? I've gotten 4 or 5 of them now. And where are they in my inventory?

your book, where all the monster you shrine go so you don't have to keep re-shrining the same cd over and over. Its just a page for that book. So, now you might be able to get monster you couldn't get before.

Check under "Data" then "Book" in your menu to see what all you've unlocked (from Book Cards, shrining, etc.)

i've got a jackinthecho in camaba's and a jellicno in warp's shops. i'm still checking for rares in the other but they all might just have a few different switches each month

spiritknight was in tochika (spelling?)

I have found the following in various shops
normaya maya/?
jackinthecho pancho/?
big-tokobot golem/?
haman maya/?

I got ingarul (garu/?) in CongaConga.

just found a jellnico bookcard in the nameless corridor so it is possible to find rares as drops too!!!!!

for some specifics

spiritknight tochika 11y 9m 1wk
was there both 1st and 2nd week left to check other area on 3rd week but nothing special

big-tokobot in grabad 12y 6m 3wk
came into town on the 3rd week saw tokobot checked agian on the 4th week no tokobot

pieripper in grabad 13y 6m 4mk

I also found an Ingarul in CongaConga. I wonder if there are specific dates for them... *tries to find date when she got it*

I have found:

Big-Tokobot (grabad)
Pieripper (grabad)
Clockwork (tiger/?) (campana)
Haman (tongue doll)
ingarul (conga)

I went to check the shop everyday, to search for any rares

i believe the 4th saucer at shop is random, while the first three is always fixed. so far i only unlock 1 new monster from shop...pretty unlucky

I haven't played that long but i've never seen a rare. Am i just unlucky or are there no rares in Garabad?

I played some more and found a Big-Takobot like 4 times in about 3 months. I stayed until i found PieRipper which took about another year.

Also in Campana i went to check for rares every week for about 6 months and have found that they seem to just have the 3 as normal and Gunbitt Hare/Durahan months at a time.