Since you are interested in making one, James A. (Jymm) Hoffman has a PDF on the basics and he may still be offering classes on how to make them. I’m sorry, but I don’t know how to do a direct link to a PDF, so try googling:
18th Century Shovels and Spades ”“ PAABA
paaba.net/Projects/JHShovels.pdf
Here is a link showing a finished shovel and spade he makes:
http://www.hoffmansforge.com/my-work/entrenching-and-gardening-tools/
To View original pictures and some original spades and shovels, this link is great:
https://www.scribd.com/document/262747317/Tools-Shovels-Spades
A page from Diderot’s Encyclopedia showing some:
https://georgeglazer.com/prints/industry/Diderot/Briqueterie-p1.JPG
Another from Diderot’s:
http://artflx.uchicago.edu/images/encyclopedie/V18/plate_18_2_58.jpeg
Here is a great link showing types of both handles and blades. BTW, the handles that look like modern ones with “D” Shape Grips are made from one piece of wood.:
https://www.nwta.com/courier/6-96/tools.html
BTW, English Gardening Spades are still being made with the “T” shape handle and 18th century style, straight, pointed blades. These are smaller than a full size spade, but can be about the perfect size to dig campfire pits and still fit in with all your other gear for reenacting. My Sister was really into gardening before she got Rheumatoid Arthritis and I bought one of those for her. I sharpen the blade for her every couple of years and it is scary how good it digs, though you have to get used to the T shape handle.
For more Reproductions,
1st Link, scroll down to :
SHOVEL & SPADE - After many years of research, we are able to offer authentic styled entrenching tools at a reasonable price. See CENC, page 268 for sample period tools. The main feature of these tools that differentiates them from most modern made ones is that the blade is almost parallel to the handle. Size of both tools is 8 by 10 inches, excluding the socket. These tools will hold up to rigorous work. Furnished without handles, which are available separately. Pointed Blade Shovel #SVL3 or Square Blade Spade #SPD3 $29.00 each
http://www.avalonforge.com/MainTools.htm
One offered by G. Gedney Godwin,
http://gggodwin-com.3dcartstores.com/Shovel-470_p_107.html
Hope this helps.
Gus