*Check with the local high school for a student with the local FFA or a 4H group who would be willing to work part time for me.
*Find a fellow homesteader who would be willing to barter services. Help me with heavy projects in exchange for garden goodies or home baked goods.
If you are unable to go down on your knees to garden, there are many tools that will allow you to still work in your garden. You can find some suggestions and options here.
And raised beds for gardening are your friend! You can find many options, even some built for being able to access from a wheelchair. Here is a quick Google image search for some ideas for you.
Homesteading can be done by those with disabilities...sometimes with the help of other people, sometimes with the help of tools, and sometimes out of pure determination and modification.