You can try looking at small camera belt cases or the case below. But from reading your post you are wanting to utilize it in a bag while recording? Might not be a good thing because the volume controls and what not are on the sides of the machine. The Zoom was intended for hand held type recordings or on location recordings where you can just lay it down and go. Go over to the portabrace website and look around as well. I remember they made something for the Tascam DR-100 so that may work or they may have something different.
I was looking for something similar recently, I found http://www.lectrosonics.com/catalogs/UniversalCatalogPages/PouchesandCarryCases.htm and there are some potentially viable options there. the BCWIRE and BCHINGED look like they might work, the BCHINGED uses 3/16" screws, not the 1/4" that the Zoom needs, however, you could probably modify either of those to do what you need. Not sure what the pricing is but it's worth looking in to.
Instead of a belt clip, you can use a neck strap. Canon has one called the Canon Metal Neck Strap 1 that works really well with the H4n. You can wear the H4n around your neck and it frees up your hands.
Lol oh man that's funny. You know I never looked hard enough at my H4N to notice the loop hole at the bottom. That's what I get for skipping through the manual. So ya I like that strap, looks great. I still prefer the belt clip as the XLR isn't in my way, but nothing compares to having it mounted on the rail system so I can actually SEE the levels. I wish they would have put that loop hole on the top versus hanging upside down with the XLR pulling on it. Or better yet they need to make a body glove with holes precut or something similar. Kinda surprised they haven't done that yet.
For me it was too much $$..and I already had a generic brand mixer bag around.
To see the levels while booming, I ended up laying mine flat in the small mixer bag. I like to have the boom going through a splitter to both channels (each set differently for safety) so I put that with the inherent connectors in the bottom of the bag, made shelf out of dense foam and put that on top of the splitter. This raised the Zoom up near the clear window of the mixer bag. I have the remote attached to the boom pole so I can start and stop while keeping hands on the pole. It's functional and also serves to make the setup look more like a regular pro setup since the H4N is usually not even visible to others...except when changing those damn batteries.
If you want a more substantial connection that that achieved by using the plastic eye on a Zoom H4n or H1, and you want ready access to all the controls, simply attach a suitable tripod plate to the unit then loop any sort of cord etc to the plate and around your neck. The Manfrotto 200PL plate has a metal tightening handle on its rear and this is ideal: http://www.speedgraphic.co.uk/quick_releases__plates/manfrotto_200pl_camera_plate/11094_p.html