I tried to search the net for this joke...and indeed it is there, but it seems to have copied and pasted from one or two sources over & over and is is a pale imitation of the longer form, which I attempt to reproduced here from memory:

..Into an apothecary shop one day walks a young Scottish military officer. He heads to the counter and asks the druggist/apothecary,(insert proper dialect if mine is not accurate)
"Excuse me, sir..but would ye be havin'..ummm...any condoms?"..."Why, of course...several brands" "And how much might they be?"..."Well, these are 50p for a box of 12...and these are 35p.."

"Have ye no got any cheaper?".."Well, here is a 3pack for 15p"...The young officer wrinkles of his forehead, thinking...then says, "Well, I'll be back", and heads off.

Twenty minutes later, he's back. "Are ye sure that's the cheapest ye have?".."Yes, I've shown you all I have."
..."Well, will ye sell one from the 3 pack?"..."One?..We don't usually break a pack...but I suppose if ye'r that hard up..".."So..how much for the one?"...."Oh, I'd have to have 8p to break the pack."

So the officer thinks again and says.."I'll be back." And off he goes. This time it is 30 minutes,,,but he does come walking in slowly..."So..8p is the best ye can do for one?", he asks hopefully. "I told you", says the apothecary firmly.."I'd be doin' ye a favor to break a package"....The young fellow reaches into his pocket(sporran?) and extracts a little foil packet which he carefully unfolds, revealing a used condom.

The apothecary says, "Hoot man, Wat be this yur'er thrustin' befor me?" .."So", asks the officer,"Do ye take trade-ins?"....

The apothecary loses patience.."NO!Ye must be daft, mon!..We do no such thing! I sell new ones, and that poor worn out thing is of NO use to me or anyone else!"

"Ah..weel, then...I'll be back," and off he goes. And this time it is 45 minutes before he returns. With a sigh, he opens the foil packet and deposits the used condom in the waste bin beside the counter and says to the glaring apothecary, "Weel, I'm sorry to have been so much trouble to you, sir, but if ye'd be so kind as to break that 3-pack...the regiment has voted..we'll be havin' a new one."