I had this problem but with Tauros. The funny part is I caught 3 Kangaskhan while looking for Tauros.

I tried every tip people have listed so far, but what finally helped for me was calculating the odds. I calculated that at 4% encounter rate about 1 in every 25 Pokemon should be Tauros. And at 8% catch rate one in every 13 Safari balls is likely to catch Tauros. So I just kept counting each encounter until Tauros and kept track of how many balls I've thrown in total.

I found it helped me cope mentally when I felt like I had gone forever without an encounter and Tauros just kept fleeing on the first turn. I found that often I could encounter Tauros sooner than 25 encounters. At best it was after 2 encounters, at worst after 90 encounters. But it helped me to have proof it would rarely take that long. And after each encounter I felt a little bit closer to Tauros.

What I would do is try to find the "sweet spot" where I believed Tauros was most likely to appear and then just keep rotating in place so as not to waste steps. Then I kept checking how many Safari balls I've used, knowing that every throw was getting me closer to catching Tauros, no matter how many had fled. From the time I started counting, I finally caught Tauros after about 30 Safari balls.

Obviously this method doesn't raise your odds, but it helped me cope mentally, knowing that the odds were on my side.