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Inova x1 is a great option. He might also like the 2AA indestructible light from Home Depot.
There are not a lot of two mode lights, anymore.
How about a xtar wk50 . Has 4 modes but does have momentary on according to a review here on BLF. Less than 8 bucks at the site linked, but only in the pink shown I think.
Just received the 3 wk50 I ordered. Lost one to the wife. She loved the color. Great little torch for less than 8 bucks.
True it does change mode on each momentary push of the switch. Once turned on its on that mode til switched off. It does have last mode memory though if left off for a couple seconds. Sorry the recommendation didn’t work out for your dad.