Sometimes you need a particular item for load-banking, but resistance heaters or electric fan heaters are actually excellent load-banks.
What do you need to do before approaching these companies?
First, you need a good, solid idea of what it is you want to achieve, and you should have a budget in mind - either of these might or might not be realistic but if you go into the discussions with an idea of what you want and how much you want to pay it's a good starting point. If it's for loadbanking - then you might need to consider the ameters and voltmetres want on the device - do you want switchable power consumption? Indicator lights?
Everything will add cost of course - but it will give you a starting point, from which you can lower the spec or increase the budget. Having one offs made will of course be very expensive - but if it's for a production run of over a hundred there should be many small companies who are willing to take on the project.
A custom electric heater or bespoke load bank is always going to be more expensive than a standard model - but sometimes there simply isn't a standard model which will do the job.
