Remember, though, the Clans are all about youth and the next generation, and have lavish budgets for trials and training. On Huntress, the only omnis were the ones used by sibkos and trainers, rather than by the experianced, bloodnamed veterans (who were past their prime). So there's every indication that at least prestege trueborn sibkos in larger Clans have all the access to omnis they need or want. Given the ease of repair omnis offer, this may not be quite as silly as it seems, especally since in the sibko one imagines few machines will be totally distroyed (both to prevent waste, and just because sibkids won't have the skills to quickly and efficantly core their opponents).
Now, the Spirits, or Cobras, or someone like that, one might think maybe not omnis. But, since the Spirits are such rigorous trainers who take such extreem pride in turning out the best, it's possible to imagine that the one or two sibkin per sibko to make it might be offered omnis to train in (makes a hell of a disapointment not to test out extreemly well and end up in a Star League relic), and the Cobras too train few enough warriors that the best might well have Kit Foxes or better to work on.
Now, in the post invasion, when the Clans are tenuiously exposed to economics, that seems to be changing. Part of that seems to be a change in training methods, and a larger number of warriors being trained (to make up for larger losses), meaning more mechs and a longer training period with training units (a new inovation for the Clans) and probably many fewer omnis.