Welcome to the Shopsmith Forum. As Dennis said check out
Shopsmith Large Format Drawings, Illustrations and More” by Everett Davis. On his google drive you will find a restored copy of the Model 10E manual that would have came with your Model 10E originally. It will be helpful in using the machine and knowing what parts you may need for replacements. The Model 10E followed by the Model 10ER was made from November 1947 through 1953. A lot of changes were made to the Model 10's during this time. 7 headstock versions, 3 carriage versions, 4 tailstock versions, original wood extension table later changed to metal. I could go on and on but you get the idea. Your Shopsmith Model 10E was made in 1948. One thing all Shopsmith multi tools have in common is the 5/8" spindle on the end of the quill.
As far as getting replacement parts check the parts list and diagrams in the manual against what you have to see what you may need. Depending on what you want to do with your Shopsmith this will help you decide what parts you may need to replace.
As far as upgrades go, if it still has the wood extension table I would recommend upgrading to the metal extension table and a fence with a rear lock. This upgrade includes, which may have to be purchased as individual parts and not a kit, a Metal Extension Table with bracket, a Tailstock for the Metal Table bracket with knobs and a fence with front and rear locks. This upgrade makes table sawing much more accurate. I currently have two restored Model 10E's, S/N 1077 and 4708 if you need any pictures for reference of the parts that came originally with yours.
Another nice item to have is a Speed Changer. Unfortunately they are expensive to buy at online auctions. You can try looking at local sales for a Model 10 with a Speed Changer and a metal extension table for those upgrades which may end up cheaper than online auctions. Just a thought.
Although the manual says it has three speeds without a Speed Changer you can actually use seven speeds. See the attached PDF I created below.
If you have any more question feel free to ask. You will always find help here.