Hopefully you have already found a solution to this but I thought I would offer some advice in case you hadn't. As you have found, travel insurers apply a limit for a single item but also a pair or set of items and therefore cover for your clubs is limited because of this.

Your selected insurer may be able to increase your cover with an additional payment but your most likely source of cover will be from you home contents insurance provider. If you have this insurance you should check with them whether you already would have cover or whether this can be included. Normally any additional premium quoted would be more competitive from your home insurers than your travel insurers.

Hope this helps.