I have only ever tempered small quantities for small batches of chocolate and this has been very successful and now need to produce larger batches - can anyone advise how to keep my tempered chocolate "in temper" so I can temper larger quantities and use throughout the day?
Reheat as often as necessary with a heat gun, or add warm untempered chocolate. As long as you don't exceed the working temperature your chocolate will stay in temper.
It sounds like your business is gorwing and that's fantastic. What you need in this case is a tempering machine. You just need to feed the machine the chocolate you use, set the right temperatures and you'll get excellent tempered chocolate. Plus think about all the time saved on tempering, re-tempering,cleaning...
If you are still tempering by hand, your chocolate will stay at your working temperature longer the larger the volume of chocolate you are working with. Reheat as needed as already suggested in the other post. There is no special trick - once you know how to temper, as you already do, it is pretty much all the same no matter how much chocolate you are working with.