You cant obtain the firmware since the Meru Networks was acquired by Fortinet a couple of years ago. Fortinet will not allow you to update the device without the controller which can only be obtained after you purchase an active licence.
Soc is P1020NSE2HFB and 2 minipcie 3t3r netcards are covered with goo in pictures and chips scraped blank for picture. Base SoC is supportabled (qoriq platform), cards to be seen.
Open the case and make "cleaner" photo, especially about any test points/diagnostic ports, and the wifi chip labels under rf shields. You may need to enhance contrast to get what was printed on chips...
Be aware that you are the (only) one owning this hardware, so you'd be the only one who could do the porting work. If you're up to that, great - if not, it's not going to do itself and chances that others will buy one and do the porting for you may not be that great.
The Broadcom BCM43460 wireless cards however throw a spanner into your plans, this is not going anywhere (so you'd have to replace the wireless cards with something else, which nukes your bargain).