This close to Halloween, you would be much better off just promoting on an affiliate basis. As a general rule of thumb, you need tobe 60-90 days out when sourcing seasonal stuff ie. July and August are the right times to be lining up suppliers for Halloween-themed items. There are various reasons for this, not the least of which being that unless you have a massive advertising budget you aren't going to be able to build meaningful levels of traffic to your site/listings in just a few weeks.
All the big retailers are out in full force with sales, most of them have affiliate programs -- BuyCostumes.com is a great one to promote (available through CJ.) I've promoted their products every year for the last few and done pretty well with it, in some cases on sites that have nothing to do with Halloween at all. Their commission ranges from 10-25%, which is easily on par with what you'll net dropshipping anyway, so there's no real tradeoff in my opinion.