best place to buy plastic blok/blocks for sj please?

I don't think they make them anymore, I couldn't find any when I looked last year.
I wanted substantial fillers and ended up buying road barrier blocks at £60 a pair.
They are great as fillers and horse don't knock them over, plus on their flat sides they make good trotting pole holders.
My best ever bargain was at a sale I went to totally unhorsy, where I stayed right until the end and bought the most amazing hard plastic containers for just 27p each. I got 21 and they make a wall, they have five cut outs on different sides to rest poles on, and are the toughest grey plastic Ive ever seen.
I wonder if the original bloks are sold under a different name now?
 
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