I bought everything for mine on Amazon - most things had the option to buy in bulk. Do keep an eye on delivery costs though - I found a number of things that were really cheap, but hit you with the P&P. If you have Prime, do a search for Prime only first.
I bought some lovely little wooden hearts to go on my invites.
I've also just started buying stuff from Wish - nothing has arrived yet, but I've seen lots of good reviews.
Have fun! x