If you just need the army drawers pattern, you can get it from Charles R. Childs:
County Cloth/C.R. Childs: army patterns, drawers...
Sources for the "canton flannel" for army drawers (a sturdy cotton flannel) include Childs, Wambaugh, and Tart.
The drawers pattern you see online from Timeless, judging solely by the image of the finished piece, looks like a pair of scrubs with some old timey modification.
As regards their shirt pattern, according to the listing, and this review, it is evidently just "old timey" and is not based on anything specifically civil war...
Pattern Review...
Though I personally have no experience with their patterns, so cannot judge their patterns or instructions, etc. I will just share that my own experience with sutlery costume patterns nearly convinced me that sewing garments was difficult. tailor's patterns (like Childs) are cut for the pieces to actually fit together, and convinced me to keep on stitching.
Childs/county cloth sells a period man's shirt pattern, with cuffs, etc., copied from the shirt of Confederate soldier Henry Hollyday (essentially a citizen's shirt). (look under CS patterns on his site). Or the simpler "Louisiana" soldier's shirt. These patterns could be used with any material, plain, checks, etc. He also has the US Army issue flannel shirt pattern if required (though cotton citizen's shirts are much more comfortable in the summer!)
BandB Tart has some excellent check shirtings on his cloth page, suitable for 1860s stuff. Wambaugh has lots too:
Wambaugh, shirtings...