Memory a bit dim on this but I do recall someone with a bike problem (suspension also, IIRC) found help in Salta, Argentina. Pretty big town, so maybe you'll have luck there either sourcing new shock or rebuilding your current one.
What shock is on there now? I believe BMW use a low budget WP shock on your bike as the standard item? Correct?
Haven't heard of suspension help in Bolivia, but who knows. A BMW dealer is gonna bone you on price for a new WP replacement and probably take over a month to get hold of.
There may be tutorials on line. With a few tools and some instruction you could probably crack open your shock and fix it .... BUT ... will need NEW seals and bushings that fit. Maybe the guys who built your shock in UK can mail a "kit" over to you? This would help any mechanic who tries to rebuild current blown shock.
Also, be sure to recharge the nitrogen, and do it correctly. You can blow out seals if too much pressure is used.

Just thought of something!
Does your bike use one of those silly Air Bladder jobs like on the standard
X Challenge? Jeeez, hope not. Those are a disaster. Maybe that's why you have another shock on there. Well, hopefully it can be rebuilt ... maybe made better than new??
Good luck! maybe someone will remember the shop in Salta.
(I could be dreaming!  )
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