Prebuilts from brands like Ducky? mechanicalkeyboards.com
DIY kits are generally best bought from their mfg's - Akko, Keychron, GMMK, Keycult.
More general retailers will have some mix of keycaps, switches, kits, maybe prebuilts and accessories - Novelkeys, Canon Keys, Mekibo, Bolsa Supply (mostly GBs), Vala Supply, KBDFans, KPRepublic (mostly caps), Kono Store, Drop (mostly caps).
To track upcoming and live GBs, at least for keycaps and keyboards - mechgroupbuys.com. It's pretty dead at the moment but I think the number of active group buys has tumbled recently due to several high profile scandals in the industry (namely Mechs & Co and Rama). Also several major keycap manufacturers piled up huge backlogs during the pandemic that are only just finally clearing up, namely GMK and Milkyway. All of that is causing there to be very few new GBs starting right now, and they can be kind of hard to find unless you're already in the communities of the designer(s) or refreshing Geekhack.
I think she is just kinda the default if you have no imagination - softspoken human female that isn't totally obnoxious.
In terms of female romance options Lae'zel is the only one who it seemed to make sense would be forward enough to try and jump your bones after just 2 or 3 days. Karlach wasn't even an option for me, she had no romance adjacent dialogue at the tiefling party. I wonder if part of that was just how late she joined up in act 1, I did get her engine "fixed" for the first time but it was one of the last things I did and I can't remember if it was before or after clearing the goblin camp.
I did really enjoy Shadowheart's arc though, especially since I generally adopted a policy to not suggest or try to interfere with the companions' quests. Just left them to their own decisions without trying to sway them, and the fact that Shadowheart chooses to reject Shar and Lae'zel chooses to reject Vlaakith (or at least hear Voss out) made for two of the most powerful moments in act 2 IMO. There is lots to like about all three of them throughout their arcs and that's part of what makes them so great.