I've made liquid pectin from citrus pips and frozen it - it works really well. Anyone living in Perth or a warmer climate where high pectin fruits are in short supply may find this easier,and possibly cheaper, than squeezing anything through muslin.
You simply collect the pips citrus pips (I get them when I am making large batches of citrus cordial, lemon butter or marmalade), pop then in a bowl with some filtered water and leave overnight. In the morning, strain the pips out and scrape as much of the jelly from the bottom of the sieve as you can. The strength depends on the # of pips and the amount of water but I find a little goes a long way