Strange, I hardly ever find any plants. I seem to only have talismans available 99% of the time
Do you have any in your inventory? If so go sell them all to Pricia. The Maca plant will always be on Maca Island. The two Ginseng plants randomly pop up in the park (sometimes they will pop up at the library or at Janet's). Each run to find all three plants only takes about 2 minutes, but sometimes it can take up to five to gather all three. My routine goes like this:
1) After selling plants, I immediately return to Estero Park and make my way to Maca Island picking up whatever I find along the way.
2) Once I take the Maca plant I begin my search for the other two. Sometimes I find one before I even reach the Maca Plant. In Fact sometimes (though rarely) I find both along the way.
3) I don't really bother crossing the river, the Ginseng Plants don't appear there. I search all quadrants of the park twice before I check the library and Janet's. It's rare that they are at those locations and sometimes it just takes a few minutes for the plants to appear. But its never long. The vast majority of the time they can be found in the park.
4) Collect everything along the way and once you have all three plants go sell them to Pricia.
There can only be one of each plant at any time. Once it is out of your inventory a new one will appear. This means that if you find a Gold Talisman, eat the Maca. You can literally collect the Maca walk into the next room, eat it and go back there will be one there immediately. Go sell your Talisman, visit the Dr. for the blowjob, sell your plants and continue.
You get $250 for the green, $600 for the red, and $1,000 for the Maca all in about 3 minutes of your time, plus whatever you find along the way.