Clock cables can alter the resulting sound that you may hear noticeably . They are important . There are several archive threads on the subject to to save repetition I suggest that you read these two:
I do make a recommendation within one of the threads and people who have followed it seem to like the result but there is good advice from others in the threads too. Several different brands are used in the community at various price points.
I will stick with my general observation that audiophile type cables asserted to be 75 ohm and intended for music signals but terminated with BNCs have been universally of poor merit when I have tried them. This lets out a lot of brands as few offer specific wordclock cables. Stick with cables intended for the purpose at least for starters. There are exceptions that prove the rule but best not to get involved just yet.
The free in the box BNC cables ( various but I seem to recall that HOSA brand are often provided) will get you going but are easily improved upon and I would only recommend them if your clock is delivered on a Saturday and it is too late to buy alternatives until Monday morning when the shops reopen 
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