Older hardware parts

I am building a network for a client and I seem to be having a hard time finding four, 4.3G pluggable SCSI-2 Fast Wide hard drives and (associated trays) for a Compaq Proliant 4500 which was donated to them. This client is a non-profit and thus hasno budget to speak of for parts. Since this server is discontinued, any idea where I can find these drives inexpensively? Even donations would be welcome….