I have oak trees all around my property and the leaves are beginning to fall.
Since I will have tons of them, if anyone who does not have access to oaks please PM me with your name/address/quantity/etc. and I will mail you some.
The leaves are from an area where no pesticides are ever used (yeah... my lawn is all weeds ) and I will be able to pick the best/just-fallen ones. Please note that I will not be responsible for any harm done to your betta if you do not follow instructions on how to prepare them for your purpose. There are numerous directions on the forums from betta-lovers experienced in diseases/illnesses/etc.
Bad thing about mailing them is that they may arrived kind of 'crushed' Crushed ones will be okay if you need them for medicinal purposes.
I recently floated a whole one in Sparkle's tank just to let it float so he has something new to 'play' with. He likes to swim underneath it and made a few small bubble nests around it. I am not using them in his tank for illness ... just to give him a toy and give him some calmness.
I brought one in the house and rinsed it off under hot tap water before putting it in his tank.
Here are some pics from 'above' his tank.