Forsythia grow by just sticking a cutting in the ground and watering it. Also, look out for people preparing to do construction work on their property. If trees or shrubs need to be removed, some folks will let you have them if you do the removal. They're often anxious to get rid of them and will give you a pile for even less than the price on the pot. Finally, don't forget to collect seeds in the early fall.
Marigolds grow easily from seeds and are easy to harvest.
Many homeowners would probably be glad to let you have a few of the dried up heads full of seeds. I have a laminate floor and like you tried all the products with no success until my grandmother gave me the perfect solution. It is using mild liquid soap and water to clean, then vinegar and water to rinse. The vinegar is the secret, as it strips the floor of all the dulling film. The first time I used it, there was an immediate difference.