Using fava bean sprouts is the fastest way to get a usable L-dopa product to take. If you are sprouting beans the fava bean sprouts have the most L-dopa at day 4 or 5 of sprouting. It seems to be most productive to soak beans for 24 hrs, then,  rinse and drain these 3 times a day for 4 more days. Then at that stage, break off any stem and set aside. Cut off any bad spots and peel the out-er skin off  of the bean to discard . Then rinse the bean well and  steam them for 1 minute to destroy bad bacteria .
I would then put the beans and the tiny stems in a food processor and blend together (or chop finely together) This you could dry into a powder to take.  Something else you could try is to freeze in a thin layer squeezed flat in a freezer zip lock and frozen , so he could use as needed, but it would keep fresh a long time.
We had good L-dopa source using the ground sprouts for “Sprout Balls”…recipe in the booklet downloadable here (Click on the Handbook on the right column here). My friend used about 8 of these a day for l- dopa supplementation.
The young leaves do not have much L-dopa…they can be eaten as salad by anyone without much effect. The buds for at the top of the stems about the time that the first flowers begin to appear on the plant (approx. 5 weeks or so after planting and each stem will get one at the top). You have to harvest the bud ball at just the right time or it opens up and just looks like tiny leaves at the top of the stem. Ants and aphids are very attracted to this part of the plant and it is good to harvest it to make the plant send out new stems from the bottom (thus more buds) and for more bean production on more stems also.
As far as going to a farmers field to pick, make sure he doesn’t spray pesticides (that he grows them organically). Sprays will make people sick along with the bees and bugs.
All you will find in the field if he is harvesting are bean pods. Any size pod is usable from very tiny to big. I would wash them. Open ones with bean inside and remove them for eating..(.they are delicious…need to be lightly steamed and taste like peas) Then juice the pods. You can freeze juice in small containers or ice cube trays to use as drink or make the Bean blob recipe in the book from the juice, adding something to thicken it like chia seeds or flax seeds ground, some salt or other seasonings you like . Line your dehydrator trays with parchment paper and drop your mixture in tiny blobs on the paper close together to dry. It works well to put mix in a zip lock bag , seal and cut off a time (like cake decorating bag)
The bean pods can be used for tincture, but you have to chop them very fine and use a press to squeeze the tincture out of them when the 4 weeks of shaking them in brandy are finished. We had to make something special to squeeze the brandy out without leaving a lot behind in the pods. Hope this helps
Love Aunt Bean
I made a large Batch of fava bourbon tincture from farm fresh organically gown fava Beans grown in Malibu. I also made fava oil for skin by soaking the inner peas, also I ground powder and made caps after drying some.
love, lynn Botanicals
Contact me if you need some tincture.