Lawrence, you will need to find a lighting distributor that caters to commercial customers, such as electricians, maintenance departments etc. You will not find what you need on the shelf at a consumer based retail store.
You must ask for a lamp socket with leads for the ELJ, or which ever lamp your enlarger requires. The sockets vary by voltage (pin spacing) and mounting configuration. The lighting distributors typically buy these lamp sockets in boxes of ten from companies such as American De-Rosa and Satco. Distributor cost is usually less than $2.00 per socket. Pull the lamp socket from your enlarger and try to match it with one of the dozens pictured in the Am. De-Rosa or Satco lamp parts catalogs.
The same lighting distributor will also stock the AV lamps by ANSI code, not necessarily by MFG description. When you ask for an ELC or ELJ, they may offer you an Osram-Sylvania, Philips, or G.E. branded version. The prices will fluctuate wildly (from $8.00 ea. to $38.00ea).
The same lighting distributor may also be a stocking distributor for Eiko, Higuchi, or Ushio, who are all fine manufactures of these types of lamps, but sell them at roughly 1/10th the cost of the big three mfgs.