You can take holly cuttings from this season's growth (new growth) in the autumn and leave them over winter to root. Take cuttings about six inches or more long, remove all but the top two sets of leaves, and bury in the soil up to the leaves, preferably adding sand or grit to make the soil well draining.
The cuttings should start to root next spring but leave them in place until the following spring when they start into growth when you can transplant into the permanent positions.
I'd say pessimistically that you should get 50% of such cuttings to take, any more being a bonus.

Thanks for that