Set “woocommerce_is_purchasable” to false for specific “$product->is_stock_status”

You are using not existing variable $product

try this:

add_filter( 'woocommerce_is_purchasable', 'command', 10, 2 );

function command( $value, $product ) {
    if ( $product->is_stock_status( 'callavailability' ) )
        $value[] = 'false';

    return $value;
}

The first parameter is actually a boolean value.