It is pretty common to find special deals where you can get a no deposit bonus. Some of the online casinos have offers for specific sites that cater to no deposit casinos. If the site is only about this, then only casinos which give those bonuses will be listed. So the online casinos that want on the site will make arrangements to offer a bonus in order to be advertised. This makes more no deposit casinos available to play at. When your looking for new places that offer the no deposit deals you may have to search a few pages in the search engine as sometimes they get bumped off the first page. Where you may miss out on some great offerings just due to the fact is you thought other sites listed all possible deals and this may not be the case.
If you want to play and do not want to deposit as soon as you join then it does take a bit of research and surfing to find all available offers. Take your time and pick only ones you think you may enjoy the most. If you sign up at every casino and never deposit then they start labelling you as a abuser as many owners have more than one casino and some have over 30 casinos they operate. Special promotions are common and can be found if you look hard enough.