Hi Andy
Sorry, but the only baggage services I know of are through Easyways
www.easyways.com or Contours, and these are bundled with their booking service (entire holiday in advance). Easyways uses a local taxi firm Jim Donald 01575-582 324 - thanks to Douglas of Easyways for this phone no.
But what about a different approach, combining travelling light with a halfway resupply point.
Don't leave any safety or weatherproof gear behind (snow, hail and high winds are possible, perhaps likely, next week) but do cut out everything else that isn't vital (especially the kitchen sink

). This is mainly a matter of deciding to live more simply for just five days and leaving behind everything that relies on batteries/rechargers, is printed on heavy paper or is an alternative to something that you are already wearing or could easily buy at the next village, such as food. Since you are taking a car, and the Trail is circular ("leaf on a stem" actually) with modest distances, you could position the car halfway as a resupply point and use a local taxi or bus to get to/from it. For example, if you leave the car at Spittal of Glenshee at the start, take the A93 back down to Blairgowrie you have then only one overnight before you get back to it to swap stuff around. After that, you'll know what else you need (if anything) for the final three days. This is simpler and cheaper than organising daily baggage transfer, as well as kinder to the environment.
You are never more than 7 miles from the nearest village, so how much clobber do you actually
need? OK, I know some folk think they can't live without mountains of gear: I tell them about my acquaintance who says that travelling light means taking three socks: two to wear and one to wash. It doesn't change their attitudes, but it's worth it for the expressions on their faces

Good luck and enjoy the Trail but please tell us how you found it idc - Jacquetta
PS to Roy: many thanks for the kind words and you're right about compass and whistle and eyes up: clearly a walker after my own heart!