You should be able to get the credit card expiration of an existing card, as long as you know the user and order:

$profile_id = uc_cim_get_profile_id($user_id);
$credit_card = uc_cim_get_payment_profiles($profile_id, $order['cim_ppid']);

You should then be able to get the expiration from:

$credit_card['cc_exp_year'] and $credit_card['cc_exp_month']

You should then be able to use your old method, no different with CIM enabled, I think.