Try to look for some local products, I mean the sleeves. There must be something produced closer than in Japan. In Germany we have a few options, pricier and cheeper, depending on the thickness (and quality in general). They usually have standard perforation that fits any binder.
For example:
We use Perfect Line, highly recommend.
Thank you Masha for the tips!
We Canadians don’t seem to have that many options available … I did a quick search on Amazon.ca. Most of the photo/postcard-sized sleeves are made in A4 size, which doesn’t necessarily fit all North American binders, even though the perforation may be OK.
Or something with a custom size (23.9 × 28.5 cm) that is slightly bigger than US letter size:
The most common US letter-size solution seems to be 2 pockets holding up to 5"×7", which is a bit large for common postcards (therefore a waste of space).
Alas, I wish our country’s population is bigger so that more manufacturers can consider our needs when making a product …
Just found a partial pack of postcards at a fundraiser yard sale today. There are only 8 of the original 30, but they’re so pretty!
Of course, I will also have to find recipients who don’t mind getting Japan-themed postcards from Canada 
I am in love with these Temple cards 
Sorry for my ignorance but what is wassi tape? Also what do you do with tiny notebooks? Looks like i may be able to use those!
Another newbie question…how is there room on the postcards for anything other than a stamp and an address? I have many things i usually add to letters but i am having problems fitting it all on a the small footprint of a postcard. Thanks in advance!
So organized! I am jelly!
Washi tape is a decorative masking tape that people here use to decorate the back of the postcard! There are many types, with drawings, colors, patterns, motifs, etc. As for the little notebooks, I used them to make a little visual diary on it by gluing old stamps, newspapers clippings, dried flowers or leaves, stickers from fruit, etc. Then I would send them to someone! Of course you can use them as you see fit. 
Here are some places you can check out on the forum:
Washi Tape Discussions - You can see some washi tapes people have bought
Back of the card decorations - You can check those washi tapes in action so you have an idea how they are used
Little Notebook Tag - Where you can send and receive those little notebooks filled with nice stuff
Welcome to Postcrossing! I hope you have a fun time with us here. 
One friend offered me these
Went to my first stamp release and stamp show, then a meetup, and then went into San Francisco and found lovely cards. I love the bear hugging California. May keep one for myself…
Picked up this cute washi tape set at Barnes & Noble the other day. Featuring lines from 3 classic books. 
Don’t step on the dog!
