Still no oil pressure

When a motor has sat without oil in or very little oil. The oil pump empties and is very hard to get primed again.
There are some tools that you can attach to a drill to prime the pump. However, it is just as easy to remove all the spark plugs and crank the engine over until it has pressure.
I had one V-8 motor take several minutes of cranking to get the oil pressure to build up.
Try it out and see if it works. The big thing is cranking it over much longer than you think you need to. It takes some time.

There are a few things that could keep oil pressure from building up;

If the pan has even a smal dent, it may block the oil from getting into the pickup and not build pressure.
If the oil pump is bad.
If the motor has a lot of deposits from not being maintained, it could have an oil curcuit blockage, such as bad bearing.
If the head gasket is bad, that can make starting up intitial pressure hard as the cooling system is pumping pressure into either the cylinders or the oil system while the oil system is fighting to start its own pressure. The cooling system does not have to overcome an empty circuit. It has imediate pressure from the pump.
The fact that the oil has to first fill the pump and do this with the vacuum of a metal to meatl seal that is not very tight makes building pressure in a new or motor with an empty mump hard.
The best advice I can give you at this point is to remove the oil pan and prime the oil pump by hand. Put the pickup in a pan of clean oil and turn the pump drive with a screwdriver or what ever works. Soon the oil will come out the top of the pump as you can tilt it and move it around to get oil in it. Some oil will drain back out. By the way use an OEM filter to make sure you have an anti-drainback valve in the oil filter. However, the oil in the pump will make a seal between the metal case and metal impeller of the pump and pri ming will be easier. It is when a pump is new or has sat so long, or other reasons, that it is pretty much dry and the seal to create suction cannot be made until some oil gets in it.
I hope this helps you out. Worst case scenario, I would empty a quart or 2 and take the valve cover off, dump oil in top end across the engine to get as much oil everywhere you can, then start it.
It is either got a problem or it does not. Engies start with a short metal to metal contact every time. The high RPM of the engine will get the pump going as it will create suction faster than a starter motor.
Take care.