Mounting tab screws fell out

That information is incorrect. Garmin Customer service should be able to offer a replacement quarter turn mount kit. See the post from Garmin here

forums.garmin.com/.../the-mounting-plate-replaceable-tabs-broke

The tech support person I talked to about an hour before that post said nothing...Is there a place online I can find those?

They are only available through customer support. As the 840/540 are still quite new I suspect that for a failure like this Garmin would want the unit back to inspect it.

I understand they might, but they're putting that inconvenience on the customer.  Not only did the device fail, they now want the customer to deal with getting a replacement and setting that up, and sending in the original.  N.G.

Just received my replacement mount after contacting Garmin Customer Service last week 

Which country?

Thank you for sharing your experience! I checked the screws on my edge 840, one was already quite loose (without blue Loctite) the other was stuck (had blue Loctite traces) I freshly glued both screws with Loctite, now it should be ok

The screws on my computer also fell out during the ride. The case is damaged and the screws are lost. I contacted support, but they offered me a device replacement for $200 because of mechanical damage (lol, the damage was caused by the absence of Locktite or a design flaw). I am very disappointed.

Upd. I managed to arrange the shipment of the set after all