I reached out to Polarpro filters and have been told that they are developing an inspire 1 specific filter set, and currently is about 4-6 weeks out.
I don't know specifically what filters, but the other sets they have for GoPro's tend to include a Polorizer,2stop ND, and 3stop ND filter.

http://polarprofilters.com/

Thank you..... If they are the same quality as their GoPro filters I will avoid them like the plague! They are crap.
SRP are decent enough though so hopefully they will come out with something in the near future.

Yeah I can't speak for their quality, i've never used them. in the bigger picture its a sign we will see more soon from other third-party companies.
and with NAB just a month away, maybe sooner rather than later.

Great news, I read on the DJI forum that PolarPro Filters http://polarprofilters.com was going to produce some filter specifically for the Inspire 1.  
I also looked all over the net for a 37mm female to female adapter ring the closest thing I found was a 55mm Female/Female Coupling Ring http://www.camera-filters.com/in ... mp;products_id=7214

Please keep me in the loop on this as, I currently have the Tiffen set and due to fact that on the Inspire 1 DJI is using 37mm male treads on the camera which require reversing any normal male threaded filter and I've noticed the the tread count is not exactly the normal for a standard 37mm lens. It's close enough that reverse mounting works for UV and ND filters mounted backwards but polarizers won't work backwards.

Great news, Mkell_CA_SF_Bay mentioned about PolarPro Filters http://polarprofilters.com was going to produce some filter specifically for the Inspire 1.  
I also looked all over the net for a 37mm female to female adapter ring the closest thing I found was a 55mm Female/Female Coupling Ring http://www.camera-filters.com/in ... fo&products_id=7214

Please keep me in the loop on this as, I currently have the Tiffen set and due to fact that on the Inspire 1 DJI is using 37mm male treads on the camera which require reversing any normal male threaded filter and I've noticed the the tread count is not exactly the normal for a standard 37mm lens. It's close enough that reverse mounting works for UV and ND filters mounted backwards but polarizers won't work backwards.

DBDagger Posted at 2015-4-11 10:18
Great news, Mkell_CA_SF_Bay mentioned about PolarPro Filters http://polarprofilters.com was going to ...

I reverse mounting 37 mm ND 8 filter on my Inspire - If you are very careful it works. In the long run I for sure hope anybody provides filters that fit perfectly and have the right weight.
The original ND 4 filter weights about 3 - 4 g - the filter (ND 8) I use weights 8 gram. The gimbal and camera behaves normal I think