Boogiepop cels have actually been around for 
while (about a year or so?)... it's just that 
they rarely appear on the market and then mostly 
on Yahoo! Japan only.

Since Usagi's House just posted a gorgeous 
Boogiepop cel for $300 on their site, I would 
suggest you e-mail them and ask them if they have 
any others (they probably do).  Describe your 
price range and such and I'm sure they'll be 
happy to help if they can:

"usagi@usagis-house.com"

Another good place to try is Anime Link, who does 
have a ton of cels which they do not list on 
their site.  E-mail them and describe to them 
your request as well:

"seruga@anime-link.com"

Otherwise, there is one final place that I know 
about (although I highly doubt that you could 
obtain the cels before Christmas)...

Anime World Star has 5 remaining Boogiepop cels 
of modest quality on their site.  However, they 
do not ship internationally, which means that you 
would have to enlist a deputy service (which will 
charge you commission on the whole transaction).

To view the cels, visit this page and examine 
items #A-218�@to #A-226:

http://www.anime-world-star.com/00cel/a12.htm

Fortunately, if you are willing to spend up to 
$100, you could grab all the remaining Boogiepop 
cels (very cheap) and pay the commission fees and 
still make it well under $100.

If you want to deal with their "official" 
overseas representative, visit here:

http://www.art-
artistbank.com/artistbank/anime/index.htm

When you contact this place, be sure to include 
the URL where you found the Boogiepop cels and 
the item codes for the cels you want.

Although some folks would say that you might as 
well as employ an independent deputy / special-
order service for about the same (or even less) 
cost.  I haven't ordered from World Star before 
so I can't recommend one option over another.