Dividers for betta tank

[roadrunner]

I found cool post on how to make dividers and I was finally ready to make it (first option) DIY Tank Dividers
but now I'm having hard time finding nice skinny black report binders. I found some at staples, but they are round (it will be a nightmare to keep them in place and I don't want to glue them). Anybody seen some black ones in dollar store lately? I would appreciate if you could let me know where.
or anybody has an idea for alternative? I don't really see myself drilling holes in plexiglass
thanx a bunch!

[roadrunner]

So I finaly found the binders in a dollar store near Roger's in surrey. Only thing is, they had only mixed colours in one package. So if you picky and would like to have all same colour, you have too keep looking or pick lots of packages. I bough enough to have all same black on the sides and I used grey on top, pink on the bottom. Bottom will be burried with gravel or sand anyway. Here are some pics of what I did so far.

[legorp]

Thnx for the post im thinking of starting a betta tank and that looks alot better than anything i was inventing in my head