Does anyone know of a conversion of these ruins from the Dragon Valley store set that made them available on residential lots? I really want to use them to build my Unseelie Court, which will be below ground mostly, but these would look amazing above ground.

I haven't played Sims 3 in awhile, but I'm pretty sure I saw them available somewhere in the Buy/Build menu.
I want to say they were in the Decor section, either under Sculptures or Misc Decor. Either that, or they were in the BuyDebug menu.

EDIT: I'm about to check right now. I might be wrong, but I'm pretty sure I saw them somewhere.

@jparks.gsp - Its not that they aren't in the menu, they are in the buy/debug menu, its that they can only be place on community lots. I want to use them on a residential lot and they aren't able to be placed on one. Unless somebody knows of a conversion or there is a mod out there that allows community objects on residential lots.

After some testing, it seems the game allows you to put certain pieces on a residential lot, but not all of them as you mentioned.
This mod is supposed to allow you to put community objects on residential lots and vice versa: http://modthesims.info/download.php?t=450059

EDIT:
When I first did my testing, it was in a new game and I just started editing a residential lot, without actually playing as a household. This is when it seemed like you could place only certain pieces but not others. However, I just tried this again, but this time picked a household. With the household, I was then able to place any ruin piece on the residential lot. It seems that the pieces I couldn't place before were ones that cost money, which I couldn't place before because there was no money to work with at the time. The pieces I tested and were able to place on a residential lot were located: Sort by Room > Outdoors > Dragon Valley.

So, it seems the mod I mentioned above isn't necessarily required for this, but you still might find it useful.

Hey thanks, I completely forgot about Buzzlers mod. I think the last time I looked at it was when people were just wanting stoves unlocked for community lot. Thats what happens when you take a few years off from a game, people go and make their old mods better and I forget they existed in the first place.

Don't know if this is of any interest, but Sandy at ATS3 converted the ruins from TS4 to TS3 here: http://aroundthesims3.com/objects/room_outdoor_10.shtml