I remember back in the old days, the Japanese render community invested fairly heavy with Poser. So did I. All those crazy props and monster characters that the Japanese poser people came up with were awesome. Royloo, Zippo, Maya-X..... 

Now that I've started in DAZ Studio, I wonder - are there any sites that give out freebies or even sell DS props and original characters by Japanese artists?

This is the link I would recommend for searching older content that may still be available:  https://poserdazfreebies.miraheze.org/wiki/Main_Page.

Also, back then you had to make your own anime and manga style stuff, nowadays there are a lot of folks who do conversions of anime characters and game characters to Daz, like Shinteo's freebies for fan art use only, of course, since they are copyright characters.