After getting "The Lathe Worlds" for Dark Heresy, one of my players from my Rogue Trader game (an explorator, of course) discovered a few bits of gear he'd want to use (such as the Atlus-pattern Jump Pack and the Enhanced Potentia Coil).

However, Rogue Trader does away with money, and the availability of the things he wants are "Adeptus Mechanicus Only".  Does this mean that the items are "Unique" or "Near Unique" or more along the lines of "Extremely Rare" or "Rare"?

I would go with Extremely Rare, unless on a Forge World where it would be Rare.

Why would the rarity change? Rarity is the same in both Rogue Trader and Dark Heresy, isn't it? It has nothing to do with costs.

The way it's described, it leads me to believe that as long as you're actually part of the Adeptus Mechanicus and can get in touch with the appropriate Forge World(s) (I suspect that in this case, it would mean the Lathes, but I can be honest and say that I don't have the book in front of me at the moment), it might as well be of Common rarity for the purposes of Aquisition checks.

The rules for Availability state specifically that the DM can adjust the availability of item depending on the setting (ex. no matter the population of the city on a feudal world, you just won't find a lasgun as there simply aren't any).

So, I would say start with the basic availability of Extremely Rare. While cruising around the Expanse, you can only acquire "Mechanicus only" items from a very specific sub-set of people. A)members of the Mechanicus who B) have the item you want and C) are willing to part with it. Since Tech Priests don't start a dime-a-dozen (compared to the total population) I would say that is a very small sub-set to be looking for. This availability is adjusted normally for population, as the larger the population the more tech priests there will be who can have the item and be willing to sell it (same idea as anything else).

However, a Forge World is a special case. Since it is actually owned by the Mechanicus, you would expect a whole lot of tech priests there. Many more chances to encounter someone with the item you desire, and more importantly, part with it. This deserves its own bonus, independant of population size, reflected in increasing the availability of the item. It would be further adjusted for population as normal (larger forges would be more likely to have the item than smaller forges).

The OP asked for an opinion, thats mine. And the rules seems to support it.

 techpriests are everywhere in the imperium. there are techpriests on the rogue traders ship, andthey  might have what youre looking for

 It probably should be looked at on a case by case basis. Look to the closest equivilent item and go from there.

HappyDaze said:

Forgeworld: Rare [the cheaper 'mechanicus only' stuff] or Very Rare [the really really really good stuff]

Hive, Imperial world, massive starbases, etc: Very rare or Extremely Rare

Anywhere else: Extremely Rare at best, often Near-Unique [the only enhanced potentia coil on that Rogue Trader vessel is probably jealously guarded by the Explorator's own Body]

Kiton said:

Thank you for all your responses; this works beautifully.  Now I have an Explorator with a jetpack bolted onto his back… oh how much fun they'll have against Ork Rokkitrangaz…