I used to have a rough go in the Supply House as a young Trooper........ I had a tough time understanding that these folks in Supply are swamped with a million different things to do and one more snotty little Trooper just wasn't on their wish list....... A couple years ago, sitting through the hellish long lineup of a Roto kitting, I started paying attention to the guys ahead of me (Which there were a great many) and how they handled themselves at the counter, and more importantly, how the SupTechs responded to them. Well hallelujah, the light came on and since that day, I have NEVER had another problem in Clothing.
My line is usually the same now, and it works for me; "Hi, how are you today? Look, I understand you can only do what you can, but I would really appreciate it if you could (Insert what I need). If you can't, that's allright, I'll try coming back another time" This bit of politeness and understanding of their situation actually seems to make them want me to leave in the same mood that I approached them in the first place - happy. 9 times out of ten (The exception being they truly are out of what I need) they come back with the piece of kit I require and I make sure I thank them for their time and help.
A year and a half ago, our clothing stores was out of Corporal shank pins for the DEU's. When I came into clothing stores for the fifth time in 3 weeks to check if new ones came in, they kept sending me packing because they were out of them. Well, on that fifth day, the Corporal working the counter recognized me as coming in 5 times in three weeks and even though I kept getting turned away empty handed, I never lost it on them and always said "Thanks for your time regardless". She took my name and number and lo and behold, the day they came in, I got a call from her saying they were in and came in and got a little handful of them. Politeness and courtesy can go a long way with Supply Techs.
Regards