Apparently you can take them to participating country toyota dealerships or rotary clubs.
www.wheelchairsforkids.org say this:
A considerable number of wheelchairs have been funded with money raised form the sale of scrap aluminium collected by supporters. Virtually any aluminium is worth collecting including old window frames, showers screens, industrial off-cuts but the most common is the common drink can.
Ring-pulls on Aluminium cans are often mistakenly thought to be made of the expensive metal Titanium and were originally thought to be useful in the making of prostheses in third world countries.
There is no reason to separate the aluminium ring-pull from its can other than that cans do take up a lot of room unless crushed and may create problems with odours and ants. Many people drop off the cans with ring-pulls attached, at our workshops. Aluminium ring-pulls are a part of our recycling drive, but it takes about 276,000 ring pulls at about $1 per kilo to raise the $100 to build a wheelchair. Many schools wishing to support our project collect only the ring-pulls and not the cans for the reasons mentioned above. In this way the students are able to be involved and become more aware of the needs of others in developing countries.
Our only collection point for recycling is at our workshops here in Wangara, Western Australia. Generally it is not economical to send any material to us by mail or carrier. Support for the project is best achieved by selling any recyclable metals to a local merchant and sending to us a cheque made out to 'Wheelchairs for Kids'.