I just literally finished sourcing all the parts on a valve for my mash tun today. And I'll tell you, without any doubt, that I regret just not buying a pre-sourced assembly from a brewing hardware site. My home depot didn't have any SS fittings, so I ended up buying them from McMaster-Carr. I bought a brass valve with SS interior components. I also ended up with 25 o-rings and 10 SS washers (nice to have extra but jeez). It was $35 for one valve assembly before shipping, and like $42 after. I realized I forgot to buy a SS hose barb so I went to my local Grainger and they wanted $20 for it (partially because it was 316 SS which isn't necessary for our purposes). I ended up just buying it from buyfittingsonline.com.
Usually I'm a proponent of DIY sourcing, but i suggest learning from our mistakes and buying a pre-assembled valve assembly.