gravity-forms-select-field.php

function acf_form_field_load( $field ) {
	$field['choices']     = array();
	$forms                = RGFormsModel::get_forms( null, 'title' );
	$field['choices'][''] = '- Select Form -';
	foreach ( $forms as $form ) {
		$field['choices'][ $form->id ] = $form->title;
	}

	return $field;
}

add_filter( 'acf/load_field/name=form', 'acf_form_field_load' );