Your search for "tubes" revealed the following:
SS-400-6 – Stainless Steel Swagelok Tube Fitting Union, 1/4 in. Tube OD, 316 SS
S$15.98
Vendor: APSS Store
View Product
SS-810-C – Stainless Steel Swagelok Tube Fitting Cap, 1/2 in. Tube OD, 316 SS
S$17.27
Vendor: APSS Store
View Product