I like that idea, DigitalZombie: instead of searching for the item itself, the avail roll would represent the search for someone to deliver and install the item.
And yes, planning ahead can definitely put one player at a sort of advantage from a game perspective. To me, that's kind of fair, because that player will invest time and energy into building his or her character, so in one way that pays off (planning what gear to get later, getting cost effective gear at chargen, deciding what to spend karma on so as to be most effective, etc).
I would love the ability to upgrade gear (my street Sam has an implanted commlink for DNI, and paying the difference between the Transys Avalon and the Fairlight Excalibur would be awesome :-), though I suspect you more meant rated items, correct?), so I'll keep hoping it'll appear in future editions.
In the mean time, the armorer check for the smartgun seems like a viable substitution for gear at least, coupled with your proposed modified avail check, at least as a house rule.