I haven't but have you thought about freezing your own gravy (leftover or made specially) for such occasions? It freezes really well.
I've tried a few of the M&S ones in pouches and had a good one a few years ago called 'poultry gravy' but they seem to change their ranges often and it isn't there now, the most recent poultry gravy I tried was in a pot, gluten free and awful.
I like the idea of freezing batches of homemade gravy. I have tried tubs from the chiller cabinet but have never found one that tastes nice. Might have a go at a Jamie Oliver style gravy (the one with chicken wings) and freeze in small batches.
Get Tesco finest fresh stock, and mix it with butter and flour that have been on the hob a couple of minutes. Takes 15 minutes max, and only 5 of actual effort - the rest is just letting it bubble and reduce. It's amazing