I researched this last year. I asked on the forum if other ElkRidges that had fireplaces could give me info. I took measurements and ended up at Lowes Home Improvement, because they carried Dimplex, the brand HL was using at the time. I found one but it was special order, and about $400, So we filed it away as an option but we haven't pulled the trigger.
You might try calling HL customer service/parts, have your vin# handy. They can probably tell you what fireplace fits there and what it may cost.
Sent from my iPhone using Tapatalk