Those AR10 receivers lol. Those links you provided one of them had them in stock when you initially posted. All out of stock now.
I'm also on the hunt for a Geissele LPK. The OpticsPlanet order I placed in December has an estimated ship date of like mid March now and if I could find a spot that has it now I'd cancel that order and get it through a place that has them right now (I ain't holding my breath). Even my local store is LOW stock on Geissele triggers which says something given their price.
I put in an email to Aero and they have no clue when THEY'LL get more stock but I set it up to get notified via email when they restock and when they do I am placing my order that minute if I can't find any prior to that.
Past that I don't have any particular parts in mind. All I need to finish my Mk18 clone is the LPK, a trigger (kinda want an SD-C from Geissele or I'll grab a simple drop in from like Elfmann), hand guard (looking to try and get a Geissele or BCM MLOK), and then the gas tube and the gas block but those never seem to sell out.
EDIT:
I ended up just cancelling the Geissele Ultra Duty LPK from Optics Planet and bought their triggerguard and the maritime bolt catch with a Leapers ambi safety selector (45/90 throw) and I'll go grab an Anderson LPK to fill out the other parts that I don't have so basically all the small springs and pins.
I still have a Leapers endplate and a Spikes Castle Nut on the way.