A/C leasing companies for the most part will not sit on stock. They order and maintain assets based on demand asked of them. The leasing company orders for the 787's are done only by request of airlines wanting them. They won't just sit on them - that's bad business. Some may have a handful of A/C sitting around, but it is unlikely.
HOWEVER! It has been known that for types with predicted high demand that they will sometimes sit on stock. The whole 73x range and the standard 32x range are a common option that leasing companies are likely to have tucked away, mainly because there is a constant demand still going on for them across the world.