Nut & bolt aisle at Ace Hardware. All sizes of spacers there. Longer bolts too. That's where I got mine.
Holding up well.
Dunno if they're American made, but probably are, since that's about all the technology we have left here.
They're a bit pricey, but I know Pingel products are made here. I have their 1" lowered jiffy stand and am looking to get their footboard spacers soon. These are a bit more than you wanted, but I think they come in 1" also.