Hi, 

Do you mean you are planting the bean seeds into gravel? They will need soil to be able to receive enough water and nutrients. 

Regardless of the planting media, garden beans will grow just fine without the inoculant as long as they get enough sunlight, water, and nutrients.

If you think you need the inoculant still, it may be hard to find a small quantity locally. You could try searching online May have to order online. You will likely find 'garden been, pea, and peanut inoculant' from seed companies. It usually has several species of
inoculating bacteria. It should include Rhizobium leguminosarum.

Follow label directions. It's very dusty so people often put slightly damp seeds in a bag with the inoculant and shake to coat right before planting.

For further reference you can visit the University of Minnesota extension page: 
Inoculating Garden Legumes

Emily