Not exactly... The Caterpillar Tunnel Max is only sold in 5-ft spacing configurations, but if you really want to have a 4-ft bow spacing tunnel, you can simply buy a slightly longer tunnel and install your bows closer together, except for the first 3 and last 3 bows. This will allow for your wind bracing to fit correctly. 
 For example, if you want a 48-ft tunnel with 4-ft bow spacing, order a 60-ft tunnel with 5-ft bow spacing and install the center bows closer together.