Could we have wearable bags specifically for bolts and javelins/throwing spears that serves the same purpose as a quiver? For bolts, you would take a bolt out and begin loading in the same line, and with throwing spears you would equip it directly.
I don't like this idea, maybe a bag but I don't think the command, pull should work for it, it takes a lot longer to load a crossbow, hence the reason you can't just pull out from a quiver or bag and load it automatically.
By the way there are things you can use for spears and throwing knives, such as sheaths.
There is a sheath location on your back as well, for those things like spears and other long weapons.