Emphasise whats' in it for them (ie marketing). It may be that the companies you've asked don't target that area. I know I saying this makes me a cynical cow, but be realistic - companies want something (a) big enough to put in their annual report, or (b) good advertising opportunity. If you're neither then they'll not help you.
Asda and CoOp supermarkets will contribute cakes etc to local charity events. Other than that, I have had best luck with local businesses - hairdresser gave a basket of products; car dealer gave a trip in a Porshe - but stuff more suitable for raffle prizes than goody bags.
Try Proctor and Gamble and Unilever. They both have a policy of helping out charities with gifts like this. Go for local companies too - the kind big enough to make free pens and keyrings etc a promotional material.
Can you link up with nay pink ribbon events? Get in otuch wiht pink ribbon PR and ask if they have any advice.
Also, use connections, however slight. Who do you know who works for one of the big companies?
I work for a Community Project raising awareness about cancer and supporting those affected. We are organising a ladies day to reach out the deprived areas of our city where cancer rates are high and screening uptake low.
The day will have a glamourous pull to it with many fun events on offer as well as valauable information about our service. We wanted to give those attending a goody bag but so far requests to the big companies have met with resounding nos!