Try e-gunparts.com
You can find 300xl ink cartridges on the internet. You can buy them directly from HP or you can buy them from amazon.com. Staples and Office Depot have them also.
You can find parts and/or a manual for an Ithaca Model 72 saddle gun in 22WMRF on many gun websites including GunBroker.com and GunPartsCorp.com. You can also find these items online at DiamondGunSmithing.com.
The logical place to look is at your local gunsmith's shop. You can probably get the parts you need online.
Watch www.gunbroker.com under "Ithaca"
Go to the "ithacagun" dot com home website for parts.
There is an online source, Numrich Gun Parts Corp - http://www.gunpartscorp.com/
Go to www.gunbroker.com enter Ithaca las scroll down and you will see someone who has a great deal of Ithaca LSA turkey gun parts for sale Hope that helps
Follow the link below to the parts diagram from the Numrich Arms website.
I would go to E-gun parts.com.they are also named Numrich gun parts corp.
e.higgins@sasktel.net , k.& e. gunparts , saskatoon,sask. pbl
SOME parts are available from Nurich, better known as gunpartscorp. check their on-line catalog of parts for the Ithaca LSA 65.
I really had no clue what a 300xl ink cartridge was so I had to look it up. It's made by HP so I would think that Staples, Office Depot and BestBuy would have them.