Basic Action Games
I agree that playing in a game where your character can't contribute in the way you anticipated is not fun and something should probably be done to rectify the situation.
I wouldn't put all of the responsibility on the DM for this though. One of the problems is that the OP designed a ninja-like character that had no plan to be able to see in the dark. This is a pretty essential consideration when you are designing a character that is meant to strike from the darkness!
When you look at the most ninja-like class in the PH, the way of the shadow monk, you see that the darkvision spell is supplied as an option fairly early on (3rd level). The other obvious ninja-like class, the rogue, can get darkvision at 8th level as an arcane trickster. Other ninja-like classes get darkvision at the following levels:
Warlock: 2nd level
Ranger: 7th level
Fighter: 8th level
Aside from that, there is also the Find Familiar trick I mentioned earlier. A similar trick can be done with the Beast Senses spell. It has a shorter duration but doesn't require your action. Like Find Familiar, it is a ritual and available to any character that takes the Ritual Caster feat.
In short, their are many ways for a human ninja to get the ability to see in the dark other than magic items.
The other obvious way is to work with the other players. Wizards, druids, sorcerers, and rangers all have access to darkvision. The spell lasts for 8 hours and doesn't require concentration. If a party has a scout that can't see in the dark, it benefits everyone to spend a 2nd level spell slot to help him out.
I think the way to go for me will probably be to buy scrolls to have someone else cast on me. I'd feel like it is too much of an imposition to ask them to give up one of the two spells they gain for leveling (and one of the high level ones at that) to gain Darkvision. Also it would be an imposition to make them burn a spell slot on it twice a day for me. With the scroll, it doesn't cost them anything to do it.