As everyone has already pointed out, Ocean monuments are fairly common if you have large oceans in your world. However, if your world (in the area around your spawn point) does not have large oceans, then finding an ocean monument is going to be challenging. With my render distance set to 13, I only find ocean monuments in oceans wider than my render distance, and the monuments are usually not close enough to land to see them from shore. Fortunately, the monuments have glowing blocks, so you can look for them at night as well as in the day.
Since you're playing in Hardcore mode, I'd advise extreme caution if you have never tackled an ocean monument before. Also, start a cow farm and bring a ton milk buckets when you go to the ocean monument so you can mine your way in. My favorite strategy is to make a tiny sky base directly above the peak of the monument and then drop sand to displace the water and then excavate in from the top. Digging your way in from underground is also very effective (if you bring a cow to keep the milk flowing).
Dr. Cyano is right, but I do have to say that I was the first to find one on the DecemCraft server because I ran and ran to find a new place for Team ULTRAMA to build our new base on the server. I found three in two days. (I say two days because it started at 23 my time and stopped when I went to bed at 1:30. ^^;
I do have to agree with the others. If your world was 1.7 before going into 1.8 than you need to find an area you have not loaded in on 1.7 and try to find one there. You do need deep oceans to do it. If you send your world seed I will try and help you find one.
Dr. Cyano is right, but I do have to say that I was the first to find one on the DecemCraft server because I ran and ran to find a new place for Team ULTRAMA to build our new base on the server. I found three in two days. (I say two days because it started at 23 my time and stopped when I went to bed at 1:30. ^^;
I do have to agree with the others. If your world was 1.7 before going into 1.8 than you need to find an area you have not loaded in on 1.7 and try to find one there. You do need deep oceans to do it. If you send your world seed I will try and help you find one.