Markbass Ninja Cab - Speaker Replacement?

[SamPlaysBass]

How hard is it to get hold of Markbass speakers replacements? 
 

Gigged my Markbass AG1000 and Ninja cab last night and it made a funny noise that wasn’t my playing for a change. It did this a few weeks back at another wedding gig - very distorted at gigging volume and the ‘bottom’ speaker seems to be throwing itself far further in its trajectory compared to the top speaker, leading me to think that the speaker/s need replacing. 
 

As a side note, I’ve tried the AG1000 on several other gigs with different cabs since that initial wobble and I can confirm that it’s not the head or the bass etc. the only difference was the cab. 
 

How tricky are Markbass spares to get hold of? I haven’t contacted Markbass yet but just wanted to know where to start looking. Ideally, I’d like to convert the cab to 4 ohm to get the most out of my Aguilar Tone Hammer 500, and I know the old NY122 cab was nearly the same spec as the Ninja 122 but with a 4 ohm load as opposed to the 8 ohms of the Ninja. 
 

Any Markbass speaker stockists happy to help?