Changing permitted uses is a difficult and time consuming process, but it can be done and is done often. It is easier to persuade the city for the zoning change if it benefits their "plan" for land use. It seems that since the property has been used this way for so many years, that you should get a favorable response just for that fact alone. You might also discuss this with your neighbors. If they do not object, that will help you in your quest.
I would need to find out a lot more information before giving you any advise. As you are probably aware the county will ask you to meet their criteria. I would love to speak with you further regarding this matter and to perhaps explore other properties that would fit your needs. Call or email me anytime: 805 709-4152 Alec@century21.com
Or you could enter into a purchase agreement with the owner which is subject to the operation becoming permitted. Or you might try to get the price discounted if you assume the liability for the lack of permit.
There are other variations, but I would strongly advise against having discussions about unpermitted operations on a public forum. You never know who's taking notes.
Please feel free to let me know if you'd like to look into your options in more detail.
You'll have to contact the city and county.
Elva A. Wormley
C2 Financial Corporation
2845 Moorpark Avenue, Suite 209
San Jose, CA 95128