I'm guessing you've probably tried searching the BDSM tag here, but what about at bakaupdates? They have advanced search by genre and you can include and exclude any category. They'll have a lot more to suggest, including hentai (which obviously you can't really find here in a huge amount), since they don't actually have mangas, only information on them.
Any good hardcore BDSM suggestions? Doesn't necessarily have to be yaoi...
Blood bank
http://www.mangago.me/read-manga/blood_bank/
http://www.mangago.me/read-manga/mud/ not really hardcore but it is amazing
http://www.mangago.me/read-manga/yoru_wa_tomodachi/
http://www.mangago.me/read-manga/partners/
http://www.mangago.me/read-manga/hoshi_no_yakata/
http://www.mangago.me/read-manga/motto_musunde_aite_waya/
http://www.mangago.me/read-manga/midnight_dog_show/
http://www.mangago.me/read-manga/ronald_no_yabou/
http://www.mangago.me/read-manga/konoyo_no_hate_made_i_love_you/
this ones kinda fit->
http://www.mangago.me/read-manga/venus_ni_seppun/
http://www.mangago.me/read-manga/tokushu_ninmu/
http://www.mangago.me/read-manga/henai_fumouhen/
http://www.mangago.me/read-manga/gintama_dj_ride_on/
http://www.mangago.me/read-manga/gintama_dj_akarui_kankin_seikatsu/
http://www.mangago.me/read-manga/hentai_play/
The first two that come to mind are sadistic boy and viewfinder
Pretty much anything by Zaria Ranmaru has elements of it, but Void and Pet Keiyaku in particular.
http://www.mangago.me/read-manga/void_zariya_ranmaru/
http://www.mangago.me/read-manga/pet_keiyaku/
Also this:
http://www.mangago.me/read-manga/toshishita_kareshi_no_renai_kanriguse/
And some djs:
http://www.mangago.me/read-manga/shingeki_no_kyojin_dj_what_s_yours_is_mine_and_what_s_mine_is_my_own/
http://www.mangago.me/read-manga/shingeki_no_kyojin_dj_kare_no_te_no_uchi/ (doesn't have bondage, but it's pretty d/s)
Oh, and since you said it doesn't need to be yaoi, Nana to Kaoru is a must if you don't mind ecchi.
http://www.mangago.me/read-manga/nana_to_kaoru/
Hoshi no Yakata
I don't know if I should be worried that I've literally read all of these
I'm guessing you've probably tried searching the BDSM tag here, but what about at bakaupdates? They have advanced search by genre and you can include and exclude any category. They'll have a lot more to suggest, including hentai (which obviously you can't really find here in a huge amount), since they don't actually have mangas, only information on them.