Of course, though it depends what you call "bulk quantity". I am going to assume home user fixing several bikes per year at most. For larger quantities, you might consider asking for special discounted offers for bulk purchases,
First of all, there are kits with all necessary parts to replace all of a bike's cables. This one goes for under $12 with free world-wide shipping.
On the other hand, every LBS sells
- shifter cable (1BGN)
- brake cable (1BGN)
- cable housing (2BGN/meter)
- housing end caps (0.2-0.7BGN)
- cable end caps (0.1BGN)
Those are all you need. Just ask them, buy some quantity, and have it at home. Also buy a dedicated bike cable and housing cutter (30BGN). When there is a problem, you reach for your tools and parts bin and 10 minutes later the cables are replaced, all by yourself.
How do bike shops deal with this? Surely they don't buy individual packs of cable for every bike do they?
They do. All cables are manufactured to a standard length, then cut after installation to fit.