It sounds like you’ve done your best to see the children, but I suspect that the conversation has understandably focused around them, rather than on what’s getting in the way of you and your wife reaching an agreement you both feel able to honour. Very often couples don’t want to revisit the past. They don’t take responsibility for their part in whatever caused the split. That, too, is very understandable. When couples decide to separate they often have their sights set on a new life, so going back over difficult and painful emotions understandably lacks attraction.
I’m going to suggest another approach. It might not necessarily change anything, but it might allow your wife to feel ‘heard’ and to open up conversation about what’s really getting in the way of you seeing your children. Being open and honest about genuinely wanting to know and understand may go some way to letting her see that you appreciate that this problem is probably not really about the practical arrangements you both clearly want for your children. Obviously, I don’t know the circumstances of your separation, but whatever they were, finding some space to understand the past and its impact on current issues can be very helpful.