Perhaps you could raffle off a one(or two) day garden overhaul by your group to a lucky winner with free plants donated by your club? Or raffle off an expensive specimen tree or plant(s).

Maybe you can offer a service whereby you go out and remove invasive species from people's yards. :-)
OR I know it's not related but one time I saw they were having a dog wash at one of the harry's farmers markets. I know that's not gardening related but it was for a fund raiser and I got a couple of stinkers to bring ya.

Why not sell fall bulbs? Some of the bulb companies have fundraiser progams.

Our garden club has a community plant swap and sale. Suprisingly, they make good money with people buying plants.
Here's how it works: you take your plants and get tickets for the "value" of your plants based on size, commonality and availability that day. You use your tickets as "cash" to buy other plants.. however, so many people bring extras that others come without trades and just buy the plants for $1.00 and up. We have people who do "incoming" and make decisions of the "value" of plants, then we have specialists who answer questions, then we have the people work the cash.

I also hold my own driveway plant sales. These are very popular in my own community and don't cost me any overhead. If you have someone in your plant club that lives in an area where gardening is popular, or people tend to be buying and fixing up older homes, then you can do very well on driveway sales. They are so fun!

Think also about offering "classes" outside of your garden club, to the public. Hands on classes which teach a variety of skills like pruning, how to make compost/leaf mold, how to mulch. Weed identification etc. This is also popular (I group many 'headings' together) with new gardeners around here. Charge by the hour and have a group.

GGG

All good ideas. Thanks so much for the help. If you think of anything else, please let me know. Our Sharpsburg Festival has always been our fund raiser, but we need to come up with fresh and new ideas. It just keeps members interested and we make scholarship $$$ for our community. Thanks again.