The shortage of $10s at the bank could be for a couple reasons, no tellar can have that much money in the cash drawer, (robbery provention reasons, etc...), so that type of request would need to be taken from the safe or vault, which often needs 2 or 3 people to go in and sign that the money is leaving the vault, a privlage that not all tellars are permited to do, so if their is not someone available to go into the vault and sign the money out, they may not be able to get you the money.
Secondly, and more likely, banks don't order large amounts of 10s, because on a daily basis, they don't give out many 10s to custormers. If you withdraw any amount of money, and got all small bills, you would be upset(unless you are a collector). So the banks always give out the biggest denomonation possiable. So the bank has no reason to have a large amount of 10s on hand.
In regards to getting 10s as change at your local convience store etc... it's much the same thing, I work at a gas station part time on the weekends, more than 50% or transactions are debit/credit. Of the cash transactions, most are done with $20 bills that have just been withdrawn from the onsite ATM(the only denomination available in this ATM). So I very rarely see $10s, I've probably gone entire shifts (100-150 custormers) and not seen a single $10 bill. Our float which is used for emergency change, is only stocked with $5s or $20s. $5s can be used for change for 10s or 20s, $20s can be used for change for 50s or 100s, so their is no need for the other denominations.