Well, you do have some time before the con to scrounge up appropriate ready-made clothing. Some parts you will have to make yourself, since I don't think you'll find all of it available in ready-made clothing. Don't forget to search Value Village, Salvation Army, and yard sales.
Remember: If you find something that's the right shape, but the wrong color, you can bleach the color away then dye it the appropriate color. Tea does wonders for making shades of brown (which is what ms Readman wears most of the time). You can also paint a rolling suitcase the appropriate shade of brown if you find one of about the right size.
Take along a color picture of your character every time you go out and look around for things that look like they would match. I'm sure you can find a few items.
