Northeast Bicycle Classifieds has some great stuff. Boston Bike Party Marketplace also has some stuff on it. There's also a gravel-specific one called Gravel & Cyclocross Trader.

Bikes Not Bombs does carry 2nd hand bikes, but probably not a gravel bike.

Hampshire Bicycle Exchange is in Western MA, but they usually have some good used inventory.

I managed to find some Amias earlier this month for about 1/3 retail price. They were from an office rental liquidation. Very comfortable and a huge improvement over the cheap chairs we had before.

Any parka with a non-tech, non-DWR exterior will be able to last a long time since you can reapply wax and usually those fabrics are harder wearing.

Fjallraven and some other brands have Parkas like this.